Dead-Rail Conversion of an MTH PREMIER NORFOLK SOUTHERN SD60E DIESEL (O Scale, 2-Rail, PS-3.0): A Follow-up

To change things up, I showed you a “simple” Dead-Rail conversion of a Diesel locomotive in my previous post. This post follows up with an even more straightforward conversion that is very similar to what I do with steam locomotives: leave the DCC decoder and electronics in the locomotive alone except to provide a plug connecting the locomotive’s DCC decoder to an external Dead-Rail DCC source instead of DCC from the rails, which in our case will come from a battery-powered radio receiver and amplifier mounted in a “battery car” (the tender for steam locomotives).

Let’s see how this is done. I will repeat some steps so you do NOT need to refer to the previous post.

The Locomotive Conversion

The first step is to remove the locomotive shell so that we can modify the “2-Rail/3-Rail switch” and convert it to a “2-Rail/Dead-Rail” switch that will maintain the ability to use track power in either DCC or DCS mode and add the ability to use DCC from an external source.

Removing the upper plastic shell was easy; remove eight screws and the rear coupler. That’s one of the beauties of MTH locomotives: they are well-designed for disassembly.

There are four screws to remove at the front and rear of the “speaker pocket” in the middle of the locomotive.
The rear coupler must be removed to access the screws at the locomotive’s rear.
There are four screws to remove at the front and rear of the locomotive. The Kadee couple must be removed to access these screws at the locomotive’s rear.

Separating the chassis from the upper shell, we see the “stand holding the switch we’ll modify.

Side view of the locomotive Interior

Repeating from my previous post: To allow track-based “2-Rail” or “Dead-Rail” Operation, we need to figure out how to get DCC from either the track (“2-Rail Operation”) or from the output of the ProMiniAir Receiver’s Amplifier (“Dead-Rail Operation”). The original 2-Rail/3-Rail switch that routes track power/signal to the PS-3.0 is shown below.

The original 2-Rail/3-Rail switch routes track power/data to the PS-3.0.

These connections were verified by using a multimeter’s resistance-measuring capability. Let’s see how this switch is designed:

When the switch is in the 2-Rail position:

  • The Right Wheels’ output is directed to the PS-3.0’s DCC Track Right by shorting the “Track Right” end post to the “Track Right” center post.
  • The Left Wheels’ output is directed to the PS-3.0’s DCC Track Left since it’s directly soldered to the “Track Left” center post.

When the switch is in the 3-Rail position:

  • The Center Rollers’ output is directed to the PS-3.0’s DCC Track Right by shorting the “Track Left” end post to the “Track Left” center post.
  • Both the Left and Right Wheels’ output is directed to the PS-3.0’s DCC Track Left by shorting the “Track Left” end post to the “Track Left” center post and the “Track Left” end post’s jumper to the “Track Right” end post on the opposite side of the switch. This connection shorts the Right Wheel’s output to the Left Wheel’s output on the center post that then goes to the PS-3.0’s Track Left!

The photo below shows how to rewire this 2-Rail/Dead-Rail Operation switch.

The original 2-Rail/3-Rail switch has been rewired for 2-Rail/Dead-Rail operation.

Repurposing this switch has the following features:

  • The output from the center rollers is disconnected and closed off. Its role was only for 3-Rail Operation.
  • The Right and Left Wheels’ outputs are located on separate posts at one end of the switch (for 2-Rail Operation in either DCC or DCS mode).
  • The Track Right/Track Left DCC outputs from the ProMiniAir Amplifier are located on separate posts at the other end of the switch (for DCC Dead-Rail Operation).
Before/After switch schematics

After remounting the newly-modified 2-Rail/Dead-Rail switch back into its stand, the Dead-Rail wires leading to the switch are connected to wires that have an external plug that will receive Dead-Rail DCC from the “battery car” we’ll describe below.

The Dead-Rail connector from the 2-Rail/Dead-Rail switch to the small external Dead-Rail DCC connector.

A plug is “snaked out” near the rear coupler to connect to the external source of Dead-Rail DCC from the “battery car.”

The Dead-Rail connections between the “battery car” and the locomotive. That’s it: two wires.

Once we screw the upper shell back in place, we are done with locomotive modifications!

All we did was modify one switch and route the new switch connections to a small plug snaked out near the coupler. It can’t be any simpler than that!

Let’s turn to the straightforward “battery car.”

Battery Car Conversion

The photo below shows the components we fit inside a “battery car:” a 14.7V battery that will just fit through the door and a ProMiniAir Receiver/Amplifier. A surface-mount Molex 21004 antenna was mounted to the external metal shell. Surprisingly, reception worked, despite the traditional practice of avoiding antenna mounts on metal surfaces.

A straightforward “battery car” contains the battery and the ProMiniAir Receiver/Amplifier, and a surface mount antenna. Surprisingly, the surface mount Molex 211140 antenna worked OK when mounted externally to the car’s metal shell.

A small hole was drilled in the bottom of the car to pass Dead-Rail DCC from the ProMiniAir Amplifier to a plug that connects to the locomotive.

The small connector exiting the “battery car” that carries Dead-Rail DCC from the ProMiniAir Recevier to the locomotive.


With these Dead-Rail modifications, the video below shows Dead-Rail Operation.

The demonstration of Dead-Rail control using a Standalone ProMiniAir Transmitter controlled by a WiThrottle app on a smartphone. The DCC is wirelessly transmitted to the “battery car’s” ProMiniAir Receiver, providing high-power DCC to the locomotive.

Final Thoughts

The Dead-Rail modifications described here maintain 2-Rail Operation in either DCC or DCS mode, which mode is selected by the DCS/DCC switch.

The 2-Rail/3-Rail switch is repurposed as 2-Rail/Dead-Rail. The DCS/DCC switch is unmodified.

If the 2-Rail/Dead-Rail switch is set to “Dead-Rail,” then the DCS/DCC switch MUST be set to “DCC” so that the PS-3.0 can interpret the DCC signal coming from the ProMiniAir Receiver/Amp in the “battery car.”

This conversion was straightforward:

  • Modify one switch in the locomotive to receive DCC from an external source.
  • Snake a connector from this switch out of the locomotive near the coupler
  • Insert a battery and ProMiniAir Receiver/Amp inside the “battery car.”
  • Snake a connector from the Amplifier out of the “battery car”
  • Connect the two plugs together and couple the car to the locomotive.

I hope this simple conversion will inspire you to try your own conversion! There are locomotives such as PS-3.0-equipped MTH that will make this process easier.

Dead-Rail Conversion of an MTH PREMIER NORFOLK SOUTHERN SD60E DIESEL (O Scale, 2-Rail, PS-3)


I thought I’d switch things up a bit. I’ve only shared dead-rail conversion posts for steam locomotives so far, but I figured showcasing the conversion of an O Scale diesel locomotive would be worthwhile. After all, not all readers share the same affinity for steam locomotives as I do! Converting a diesel presents a few unique challenges compared to steam locomotives, which makes it all the more interesting.

I was searching for a 2-Rail MTH diesel locomotive that didn’t require wheel and coupler conversion and provided a PS-3 for DCC dead-rail operation. Fortunately, I found what I was looking for on eBay – the MTH Premier Norfolk and Southern SD60E Diesel (MTH 22-20596-2) at a reasonable price, which ticked all the boxes. This choice allowed me to focus on a more straightforward dead-rail conversion, emphasizing incorporating battery power and a small but powerful (13A) ProMiniAir Receiver, with minimal modifications required. I opted for MTH because of its rich, DCC-accessible features, including lighting, sound, and smoke, and its maintenance-friendly design, making it relatively easy to open up.

First Impressions

I had to open up the locomotive and look inside to develop my dead-rail conversion plan. While MTH provides exploded drawings of some locomotives on their parts site, unfortunately, they are not yet available for the MTH 22-20596-2 model.

Notwithstanding the lack of good diagrams, removing the upper plastic shell was easy; remove eight screws and the rear coupler, and you’re in!

There are four screws to remove at the front and rear of the “speaker pocket” in the middle of the locomotive.
The rear coupler must be removed to access the screws at the locomotive’s rear.
There are four screws to remove at the front and rear of the locomotive. The Kadee couple must be removed to access these screws at the locomotive’s rear.

Separating the chassis from the upper shell, we’re confronted with a very crowded interior (see photos below)!

Side view of the locomotive Interior
Top view of the locomotive interior

The interior space is narrow and jam-packed with two motors, a PS-3 board, switches, lights, and wiring.

Two conveniently-located switches are shown below.

Two top-mounted switches offer good repurposing opportunities.

Based on this examination, I made the following observations:

  • I could not figure out how to place a battery in this space. Even flat batteries (0.2 to 0.3″ thick) would not fit!
  • The 2-Rail/3-Rail switch could be repurposed as a 2-Rail/Dead-Rail switch, making it feasible to maintain 2-Rail DCC operation and add DCC Dead-Rail.
  • The DCS/DCC switch could be repurposed as a Battery Power ON/CHARGE switch.
  • Later on, I will demonstrate that it is possible to fit the Receiver and Amplifier of the ProMiniAir inside the shell.

To combine power and control of the locomotive, I had the option to set up the ProMiniAir Receiver in the trailing car along with the battery and send track-level DCC from the ProMiniAir Receiver to the locomotive instead of DC power. But for this post, I placed the ProMiniAir Receiver inside the locomotive and connected it to battery power from a trailing “battery car,” creating a straightforward battery-powered setup.

I will show in a future post how to locate the ProMiniAir Receiver/Amplifier in the “battery car” and supply the locomotive with the DCC output of the ProMiniAir Receiver’s amplifier.

Based on these observations, let’s get into the dead-rail conversion details.

Dead-Rail Conversion

To allow track-based “2-Rail” or “Dead-Rail” Operation, we need to figure out how to get DCC from either the track (“2-Rail Operation”) or from the output of the ProMiniAir Receiver’s Amplifier (“Dead-Rail Operation”). The original 2-Rail/3-Rail switch that routes track power/signal to the PS-3 is shown below.

The original 2-Rail/3-Rail switch routes track power/data to the PS-3.

These connections were verified by using a multimeter’s resistance-measuring capability. Let’s see how this switch is designed:

When the switch is in the 2-Rail position:

  • The Right Wheels’ output is directed to the PS-3’s DCC Track Right by shorting the “Track Right” end post to the “Track Right” center post.
  • The Left Wheels’ output is directed to the PS-3’s DCC Track Left since it’s directly soldered to the “Track Left” center post.

When the switch is in the 3-Rail position:

  • The Center Rollers’ output is directed to the PS-3’s DCC Track Right by shorting the “Track Left” end post to the “Track Left” center post.
  • Both the Left and Right Wheels’ output is directed to the PS-3’s DCC Track Left by shorting the “Track Left” end post to the “Track Left” center post and the “Track Left” end post’s jumper to the “Track Right” end post on the opposite side of the switch. This connection shorts the Right Wheel’s output to the Left Wheel’s output on the center post that then goes to the PS-3’s Track Left!

The photo below shows how to rewire this 2-Rail/Dead-Rail Operation switch.

The original 2-Rail/3-Rail switch has been rewired for 2-Rail/Dead-Rail operation.

Repurposing this switch has the following features:

  • The output from the center rollers is disconnected and closed off. Its role was only for 3-Rail Operation.
  • The Right and Left Wheels’ outputs are located on separate posts at one end of the switch (for 2-Rail Operation).
  • The Track Right/Track Left DCC outputs from the ProMiniAir Amplifier are located on separate posts at the other end of the switch (for Dead-Rail Operation).
Before/After switch schematics

Look at the DCS/DCC switch (see the photo below).

The original DCS/DCC switch

The two black wires are NOT shorted together for the DCC switch setting, sending logic to the PS-3 that it should operate in DCC mode. Conversely, if the switch is set to DCS, the two wires ARE shorted together, sending logic to the PS-3 that it should operate in DCS mode. So, all we need to do to ensure permanent DCC operation for either 2-Rail or Dead-Rail operation is disconnect the switch’s two black wires and close them off so they can’t short to each other or anything else.

We can repurpose this switch to provide battery power to the ProMiniAir Receiver/Amp or enable the battery to charge through an onboard barrel plug. The CHARGE switch setting is reserved for future expansion and has not been implemented. The battery Ground is directly connected to the Power “-” of the ProMiniAir Receiver/Amplifier.

The DCS/DCC switch has been repurposed as a battery power ON/CHARGE switch.

After repurposing the switches, they were reinstalled, as shown below.

The repurposed switches are remounted as shown.

With the switches reinstalled, we focus on mounting the ProMiniAir Receiver and Amplifier in a location that avoids mechanical interference with installed components.

Since the locomotive shell is plastic, the antenna can be internally mounted. To reduce the mechanical interference from an 82 mm whip antenna, I replaced it with a Molex 211140 “surface-mount” antenna (found at Mouser or DigiKey) mounted in the cabin area.

After a bit of trial and error, the mounting locations of the ProMiniAir Receiver and its “tethered” Amplifier are shown in the photo below. The tethered design provides improved flexibility for mounting in crowded conditions.

Mounting locations for the ProMiniAir Transmitter and its “tethered” Amplifier.

Routing of battery power and Dead-Rail DCC signal wiring to prevent interference with closing up the shell is always challenging. My solution is shown below.

Routing of the added battery power “+” and “-” and the ProMiniAir Receiver’s DCC Track Right/Left output.

Note the battery power wires “snaked” out between the bottom of the chassis and the rear truck, which connect to the “battery car” shown in the next photo.

Battery power connection between the “battery car” and the locomotive.

The “battery car” I used had a metal shell that did NOT have a removable top or bottom, so I was forced to fit a battery through the small door opening in the side of the car. Fortunately, I had an oddly-shaped battery from MTO (see here) that often fits in tight quarters where other 14.7V battery packs will not. This is a very valuable, if expensive ($80), battery configuration to have on hand for dead-rail installations.

The TRAIN-10 LI-ION 14.8V/3.0Ah battery from MTO Batteries. Its unusual shape helps it fit in many situations where other 14.7V battery packs will not.

The photo below shows the battery installed in the “battery car.” The battery power wires were passed through a small hole I drilled in the bottom of the car near the coupler. Because the battery is asymmetrically-shaped, its uneven weight distribution is counterbalanced by a steel weight strategically placed at the other end of the car.

The unusual shape of the battery facilitated squeezing it through the car’s side door.


The first demo shows we retained the standard track-powered, 2-Rail DCC Operation. The 2-Rail/Dead-Rail switch is set to 2-Rail to route the track’s DCC to the PS-3. The Battery power switch is set to CHARGE (OFF) to prevent draining the battery by powering the onboard ProMiniAir Receiver that is not providing DCC to the PS-3.

Demonstration of track-based, 2-Rail DCC Operation.

The video below is a demonstration of the Dead-Rail Operation in action. Battery power is provided by setting the Battery Power switch ON, and Dead-Rail DCC is sent to the PS-3 board by setting the 2-Rail/Dead-Rail switch to Dead-Rail. A Standalone ProMiniAir Transmitter (see this page for a detailed description) integrated with a WiFi-equipped EX-CommandStation provides a WiFi connection to an iPhone’s WiThrottle app. The commands from the WiThrottle app are converted to DCC by the WiFi-equipped EX-CommandStation. Then the ProMiniAir Transmitter connected to the EX-CommandStation transmits this DCC to the ProMiniAir Receiver onboard the locomotive.

A demonstration of Dead-Rail Operation

Final Thoughts

The most challenging part of the installation was finding a location inside the locomotive for the ProMiniAir Transmitter and its Amplifier that did not mechanically interfere with the rich set of installed components. Also, routing the added battery power and Dead-Rail DCC signal wiring was challenging. Physical examination is essential for developing a dead-rail conversion strategy, but some trial and error was required in the end!

In a future post, I will show how to mount the battery and the ProMiniAir Transmitter/Amp inside the “battery car” and simply output full-power DCC from the ProMiniAir Receiver/Amp to the locomotive, eliminating the hassle of finding locations for the Receiver and its attendant battery power wiring inside the locomotive. This configuration is much like what I do with steam locomotives: install the battery and ProMiniAir Receiver/Amp in the tender and then provide high-power DCC to the decoder inside the locomotive.

One intriguing possibility is that this option can provide high-power DCC to two or more locomotives simultaneously. This is because DCC inherently sends commands to multiple locomotives, and the 13A Cytron amplifier has enough power to handle multiple locomotives.

Dead-Rail Conversion of an MTH UP 4-12-2 2-Rail locomotive with the New, Smaller ProMiniAir Receiver

I have posted several dead-rail conversions of O scale 2-Rail MTH steam locomotives equipped with a PS-3.0 controller capable of operating in DCC mode. These locomotives are convenient for dead-rail conversion because they come fully equipped with good sound, lighting, and smoke effects – all controllable with DCC. However, I have received numerous questions asking for clarification.

So, what’s new in this post?

The goals of this post are to show off a dead-rail conversion with my new, much smaller ProMiniAir receiver (1.1″ x 0.8″) coupled to a small DCC amplifier, the DRV8871 (1.0″ x 0.8″) and to explain the conversion strategy for O scale, PS-3.0-equipped MTH locomotives. I have chosen the PS-3.0-equipped MTH UP 4-12-2 2-Rail locomotive (MTH 22-3641-2) because it has a small, crowded tender, making for a challenging installation of the required dead-rail components: battery, ProMiniAir receiver/DCC amplifier, antenna, switches, and charging plug.

Some conversion details, such as power connections, are left out to reduce cluttering the critical points.


The photo below shows what we are up against: a very crowded tender!

The original, very crowded tender electronics

The challenge is how/where to locate the dead-rail components.

Dead-Rail Conversion

Since this locomotive is fully configured for lighting, sound, and smoke effects, and all control electronics are in the tender, I did not modify the locomotive!

We’ll turn our attention to the tender.

The most challenging aspect of this conversion is battery location. After some fiddling and considering other battery configurations, I decided on a flat 14.8V Tenergy battery mounted in the tender, as in the photo below.

Battery location using a 14.8V Tenergy battery

This location required slightly bending the PS-3.0’s heat sink to provide battery clearance.

I also moved the speaker platform forward and removed the plastic speaker enclosure to make room for the battery.

I moved the speaker platform forward to provide room for the battery.

The wiring of the 2Rail/3Rail switch is at the heart of our conversion. Since we will not operate on 3-rail track, we will repurpose the 2Rail/3Rail switch to retain the original 2-rail track-powered operation or use the new battery-powered amplifier output connected to the ProMiniAir receiver. See the diagrams below for the original and final wiring for repurposing the 2Rail/3Rail switch.

The original switch wiring for 2-rail operation. The right 2RAIL post is not connected!
The original switch wiring for 3-rail operation. All wheels become “Track Left,” and the center-rail pick-up rollers become “Track Right.”
The final switch wiring for 2-rail operation. Track-based “Track Left” and “Track Right” are fully retained.
The final switch wiring for radio-control operation. Now the ProMiniAir receiver’s DCC amplifier outputs supply “Track Right” and “Track Left” to the PS-3.0.

I modified the wiring to the 2Rail/3Rail switch to accommodate DCC inputs from the ProMiniAir receiver’s amplifier. The photo below shows the first step: moving the gray wire soldered to the right center post of the 2Rail/3Rail switch to the front right post.

The next step is the hard part: figuring out the re-wiring required. To aid in the discussion, let’s talk about the capabilities of the MTH PS-3.0 controller. This board is designed to pick up signals through the locomotive and tender’s wheels and, if operating on 3-rail track, the center-rail pick-up rollers. To accommodate either 2-rail or 3-rail operation, MTH provides a 2Rail/3Rail switch on the underside of the tender chassis.

Consequently, when you set the switch to “2Rail”, the gray wires, which are electrically connected to the left track, provide input to the “Track Left” of the PS-3.0.

Next, the gray wire directly connecting the “Track Left” input to the PS-3.0 board is separated from the other gray wires and soldered to the right-center post of the 2Rail/3Rail switch. Now, the center-right post provides the “Track Left” input to the PS-3.0 from rail “Track Left” when you set the switch to “2Rail.”

Moving the gray wires and creating a single Track Left input to the PS-3.0
The Track Right (red)/Left (gray) connections to the 2Rail/3Rail switch to the PS-3.0 board

Since we will NOT be operating in 3Rail mode, we can repurpose the 2Rail/3Rail switch’s 3-Rail connections to provide the DCC inputs from the ProMiniAir receiver’s DCC amplifier.

I first removed the wiring on both of the 3Rail posts on the switch.

Removal of the 3-Rail wiring connections to the 2Rail/3Rail switch. After removal from the switch post, the two black wires MUST be connected to ensure that rail-based “Track Right” is supplied.

I sealed off this wiring, preserving the connection of the two black wires since they both contribute to “Track Right” from the locomotive or tender wheels.

Sealing off the 3-Rail wiring

Then, I soldered two wires with a plug to these “3Rail” switch posts that will connect to the DCC Track Right/Left outputs of the ProMiniAir receiver’s DCC amplifier. With this modification, when the switch is set to this position, it connects the PMA amplifier’s DCC output to the PS-3.0. This now completes the conversion of the 2Rail/3Rail switch to a 2Rail/RA (for radio-generated signal) switch. That was the hard part.

Wiring for DCC inputs from the ProMiniAir receiver’s DCC amplifier so that the “3Rail” switch setting now becomes the selection for “Radio Control DCC.”

The signals originally picked up from the rails come in two “languages” that the PS-3.0 controller understands: DCS and DCC. To accommodate this capability, MTH provides a DCS/DCC switch on the underside of the tender chassis. The DCS commands are a proprietary MTH invention and, for our purposes, do not interest us. DCC is important to us since the ProMiniAir receiver is designed to receive wireless DCC commands, which are an NMRA standard.

We can set up the wiring for permanent DCC operation and repurpose the DCS/DCC switch for Battery ON or Battery Charging. When you set the unmodified DCS/DCC switch to “DCS,” the two black wires activate DCS mode, which we no longer need. When you set the DCS/DCC switch to “DCC,” these two wires are not electrically connected, which is what we want permanently.

The first step is to remove these two black wires and close them off to prevent them from shorting together.

Removal and insulation of the DCS wires for repurposing the DCS/DCC switch as a Battery ON/Charging switch.

Then, three wires are soldered to this switch:

  1. Center posts: Battery +. This post provides battery power that will either supply power to the PMA Rx and DCC amplifier or receive charging power from the charging plug, depending on the switch position.
  2. Back posts: PMA Rx/DCC amp power +.
  3. Front posts: Charging plug +
Final connections for the switches

The right and left posts are soldered to each wire to ensure a low-resistance, high-amperage connection. The rest of the power connections are standard and not discussed here.

OK, we’re finished with all wiring modifications; now, let’s turn to adding the antenna and charging plug by first drilling holes in the bottom of the tender’s chassis and mounting the antenna and charging plug (see photo below).

Antenna and charging plug mounts, and repurposed switches

The antenna mount has a wire connection carrying RF output from the antenna to a U.FL connector plugged into the ProMiniAir receiver.

The charging plug has a “+” power connection wired to the battery ON/Charging switch. All power “-” connections are on the “-” posts of the charging plug.

Finally, I mounted the ProMiniAir receiver and its DCC amplifier over the speaker after removing the plastic speaker cover to provide sufficient battery clearance.

Mounting of the small ProMiniAir receiver and DCC amplifier

The small size of the ProMiniAir receiver and its DCC amplifier make this mounting strategy possible.


The video below shows the “proof in the pudding,” The locomotive is controlled by the new stand-alone ProMiniAir transmitter integrated with a WiFI-equipped EX-CommandStation that receives throttle commands from a smartphone app.

Demonstration video using WiThrottle app connected to PMA transmitter integrated with a WiFi-equipped EX-CommandStation that transmits to the onboard ProMiniAir receiver.

Dead-Rail Conversion of an MTH 2-Rail O Scale 4-6-2 K-4S

Presents the dead-rail (battery power, radio control) of an MTH O scale, 2-Rail K-4s steam locomotive with PS-3.0.


I obtained this 2-rail O scale MTH 4-6-2 K-4S (MTH 20-3473-2) on eBay circa November 2020. This model is unusual because it’s a 2-rail version with “scale wheels” and is equipped with a PS-3.0 control board that can operate in either DCS or DCC mode.

Box information on this locomotive

The Good News: No extensive 3-rail to 2-rail conversion was necessary, and no new DCC decoder was required.

The Bad News: This locomotive contained a PS-3.0 board in the tender I had not seen before. Also, this was my first conversion of a 2-rail MTH locomotive, and I had a few issues to learn!

Close-up of MTH PS-3.0 board for the MTH K-4s

Well, let’s seen how to proceed to convert this loco to DCC dead-rail operation.

Analysis of the Electrical Connections

I’ve done several MTH 3-rail conversions with PS-3.0 boards. Still, this locomotive was designed quite differently: it has a switch to select 2-rail or 3-rail operation (a potential problem) and another switch for DCS/DCC operation (easy to take care of).

Bottom view of tender showing switches and electrical pickups. Before dead-rail modification, the grey wire connected the rear left wheels’ voltage to the tender frame, and the brass spring connected the front right wheels’ voltage to the black wires inside the tender.

This is a bit complicated. With this original design, the tender frame assumes the voltage from the tender’s uninsulated rear left wheels (whose right wheels are insulated) via a grey wire connected to the tender frame, which under 2-rail operation is “DCC track left” inputs on the PS-3.0 board. The right track’s voltage is picked up through the copper pickups connected to the tender’s uninsulated front right wheels (whose left side is insulated) and is connected by black wires inside the tender. In 2Rail operation, the 2Rail/3Rail switch will connect these black wires’ voltage to the “DCC track right” on the PS-3.0 board.

Under 3Rail operation, the left/right rails are connected electrically as ground or “DCC track left” (and the frame is now either ground or DCC left rail voltage). A grey wire from the locomotive (which is electrically connected to the locomotive’s center roller pickups) is connected as “hot” or “DCC track right.”

In the original design, several grey wires are connected to the tender frame to pick up the “DCC track left.” Our job is to completely isolate both DCC track right and track left so that the DCC amplifier we add will be the only source of DCC, completely isolated from the tender frame, which will become our battery ground.

We always want to operate in DCC mode, so we need to disable DCS operation permanently.

The following images demonstrate my modifications to isolate all DCC from the frame and permanently enable DCC operation.

These images show several important conversion steps:

  1. Cut and seal off the two wires connected to the DCS/DCC switch. This will permanently enable DCC operation.
  2. Cut and seal off the grey and red wires to the center posts on the 2Rail/3Rail switch to ensure the DCC track’s total isolation right and left from any other electrical connections. This step will ensure no unexpected connections because of this switch’s setting.
  3. Disconnect the two grey wires mounted to the tender frame by one of the mounting screws holding the PS-3.0. One of the grey wires goes to the underside connector on the PS-3.0 board, and it needs to be connected to the DCC Amplifier’s “DCC Track Left” output. The other grey wire electrically connected to the tender’s left wheels should be sealed off. This step electrically isolates the tender frame from any other electrical connections, allowing it to act safely as a ground.
  4. Provide DCC “Track Right/Left” connections from the DCC amplifier (which we will add) to the two grey (DCC Track Left) and two red (DCC Track Right) inputs on the PS-3.0 board. We mentioned one of these connections in step 3, and the other pair of DCC “Track Right/Left” inputs go to the “Track” connector on the side of the PS-3.0 board.
Wiring modifications to isolate DCC from the tender frame and permanently enable DCC operation
Isolation of DCC track left from the tender frame

We need to move the PS-3.0 board forward slightly to make room for the battery, antenna mounting, battery switch, and charging plug. Also, we need to bend down the right side of the PS-3.0 board to provide sufficient clearance for the RF receiver/DCC amplifier that will be mounted on the inside top of the tender shell above the PS-3.0 board.

Also, I removed the two super-capacitors on the PS-3.0 board. The locomotive will then immediately turn off when battery power is turned off: we have no worries that power will be temporarily interrupted as with track power. I like the locomotive to turn off when I disconnect the power. This is not a required modification!

Moving the PS-3.0 board forward to accommodate the battery
Cuts of 2Rail/3Rail switch wires and charging plug mount
The 2Rail/3Rail switch center posts are disconnected
New DCC connections from DCC amplifier to two plugs on the PS-3.0 board
DCC connection to the underside of the PS-3.0 board. This image’s purpose is only to show one of the two plugs where DCC inputs to the PS-3.0 board.

Dead-Rail Additions

The tender modifications to add a 14.8V LiPo battery, antenna mount, battery switch, and charging plug can be seen in several images above. There is nothing unusual about these additions.

I used a Tam Valley Depot DRS1, Mk IV receiver with a U.FL external antenna plug rather than my ProMiniAir receiver and separate DCC amplifier because of space considerations. The Tam Valley’s DCC “Track Right/Left” outputs are connected directly to the two “track right/left” inputs on the PS-3.0 board (on the side and bottom connectors of the PS-3.0 board), as shown in the images above.

Conclusions and Warnings

I cannot emphasize enough the need for complete isolation of the tender frame ground from the DCC voltages output by the DCC amplifier that provides inputs to the PS-3.0 board. If you inadvertently leave a connection of tender frame ground to DCC left (from various grey wires), you may cause a severe short circuit, or the PS-3.0 board will not operate properly. Trust me, I know from a couple of bitter experiences…

Still, this was a fun and reasonably-easy dead-rail conversion, especially so since I didn’t need to modify the locomotive at all.

Here’s the final video of the fully assembled dead-rail locomotive. The PS-3.0 provides a number of DCC functions including:

  1. Directional lighting on/off (F0)
  2. Bell (F1)
  3. Horn (F2)
  4. Start-up/Shutdown (F3)
  5. Passenger/Freight Announcements (F4)
  6. Marker/cabin/firebox lights on/off (F5)
  7. Speaker volume (F6)
  8. Smoke unit on/off (F12)
  9. Smoke unit volume control (F13)
  10. Numerous other features (F0 through F28 are all active). See the Users Manual for extensive details.
Locomotive with final dead-rail installation

Thanks for dropping by!

Dead-Rail Conversion of an MTH 2-8-8-8-2 Virginian Triplex


This post describes my most difficult dead-rail conversion to date: an MTH O scale 2-8-8-8-2 Virginian Triplex (MTH product number 20-3101-1) that I purchased on eBay circa September 2019. Previously, I converted a Sunset 3rd Rail Allegheny with an MTH Proto-Sound 3.0 board to dead-rail. Still, the Triplex was my first complete dead-rail conversion of an MTH locomotive to 2-rail operation, which included lathe turning high-profile wheels to approximate an NMRA RP-25 flange profile (also see NMRA standard S-4.2) so that the locomotive would operate reliably on track meeting NMRA standard S-3.2.

Box details
Locomotive side view
Tender side view

The inside view of the tender below demonstrates a significant challenge: space is very tight with the Proto-Sound board and the prominent speaker consuming a large part of the tender’s internal volume where we need to install additional dead-rail components: DCC-compatible RF receiver; 14.8V LiPo battery; and switch, charging, and antenna wiring.

Inside view of the tender: Note the battery cradle, the space-consuming speaker, and the end-of-tender smoke unit.

The strategy starts to emerge:

  1. Replace the Proto-Sound 2.0 (PS2.0) board with a PS3.0 board that can operate in DCC mode.
  2. Remove the original rechargeable battery and its cradle and locate the 14.8V LiPo battery pack there.
  3. Remove the large speaker and replace it with a smaller 4-ohm speaker so we can make room for the 14.8V LiPo battery pack and the Airwire CONVRTR-60X DCC-compatible RF receiver that operates in the 902-928 MHz ISM band on Airwire channels 0-16.
  4. Lathe down the high-rail wheel flanges to approximate an NMRA “RP-25” profile for 2-rail, dead-rail operation.

An advantage of this strategy is retaining almost all of the control the PS2.0/PS3.0 provides, including the directional head/tail lamp, marker lights, cabin lights, flickering firebox, sound, and fan-driven smoke units.

Proto-Sound 3.0 Conversion

The first step of the dead-rail conversion was easy: replacing the Proto-Sound 2.0 board with a Proto-Sound 3.0 (PS3.0) board from Ray’s Electric Trainworks. As I have mentioned in other posts, working with Ray Manley is a great pleasure. I sent my PS2.0 board as a trade-in to Ray, and he took care of the rest, providing me with a fully-functional PS3.0 board, complete with DCC capability.

The heatsink for the PS3.0 board necessitated drilling and tapping a new mount hole with a spacer, as shown in the figure below.

New Proto-Sound 3.0 heatsink mount with a spacer.

The following photos show the original electrical power inputs to the PS2.0 board and their modified connections for the replacement PS3.0 board.

Original power connections to the Proto-Sound 2.0 board.

As you can see below, the AC power from the center rail pick-up (hot) and the outside rails (ground) were disconnected – we will be getting our power from a 14.8V LiPo battery pack in the tender. In this case, there is no Constant Voltage Unit, so no Battery +(14.8V)/Battery -(Ground) connections are required.

Locomotive power connection modifications. There is no Constant Voltage Unit in this locomotive, so the B+/B- wires indicated above are NOT used.

The AC power connections in the tender are also disconnected, and the power inputs to the PS3.0 connect to the switched battery power. The Battery +(14.8V)/Battery -(Ground) connection on the wiring harness was NOT required.

Tender power connection modifications. There is no need for B+/B- power supply to the locomotive.
Power input modifications for the PS3.0 board. The DCC A/B input power comes from the connection to the Airwire CONVRTR-60X DCC-compatible RF receiver.
Final wiring connections

Locomotive Electrical Modifications

There were two aspects to the electrical modifications in the locomotive:

  1. Headlamp replacement
  2. Electrical power supply

The original headlamp was a power-hungry incandescent bulb. An LED with a polarity-independent plug from Evan Designs was used to eliminate the need to determine the polarity of the original headlamp wiring.

Headlamp LED replacement details

The power-related modifications consisted of removing the center-rail pick-ups, which is very easy on MTH locomotives and disconnecting any wiring to the center-rail pick-up (hot) and the outside rails (ground).

The original center-rail pick-ups. The “Center-Rail Pick-up” is disconnected.
The center-rail connection underneath the motor is disconnected

Battery Installation

Battery installation was very challenging since the only practical placement location was the original rechargeable battery and its cradle mounting beside the PS2.0 board. A special-order 2x2x1 14.8V, 2600mAh (38.48 Wh, 5A rate,  LxWxT: 133 mm x 40 mm x 25 mm) LiPo battery purchased from provides the one cell-diameter thickness required to fit the battery pack between the PS3.0 board and the tender hull.

Original rechargeable battery and cradle location. The speaker volume control potentiometer was moved to accommodate the more extended 14.8 V LiPo replacement battery pack.
Volume control potentiometer. It was moved from its original location, and UV glue provides stress relief to prevent breakage of the very fine wires.
Final location of the volume control potentiometer. UV glue holds the potentiomenter in place.
Final battery location. Velcro attaches the battery to the side of the PS3.0 board.

Mechanical Modifications

In MTH steam locomotives, the wheel axles insert into a solid cast chassis frame, so the driver wheels must be pulled off the axle before machining the high-profile wheels to approximate an RP-25 profile that is compatible with two-rail, dead-rail operation.

The driver wheels must be pulled off the axle for machining after the removal of the side rods. The axle and wheel are scribed to maintain proper “quartering.”
A wheel puller separates the driver wheel from the axle.
Comparison of lathe-cut and unmodified high-profile wheels. The high-profile flanges were lathe-cut to approximate an RP-25 profile for 2-rail, dead-rail operation.

Tender Mechanical Modifications

The tender’s mechanical modifications involve adding a Kadee 740 coupler and accommodating additional dead-rail electronics.

Coupler Modifications

The original coupler pivot, rather than using a frame-fixed mounting, was used to mount a Kadee 740 coupler. This strategy ensured that tight curves would not bind the coupler.

The original coupler assembly

A Kadee 740 coupler was mounted on the original coupler pivot, as shown in the Figure below. The brass screw heads were ground down to provide clearance with the tender frame.

Modified coupler assembly for a Kadee 740 coupler

Additional Dead-Rail Electronics

The added dead-rail electronics include the charging plug, the ON/OFF/Charging plug, a smaller speaker, and the antenna mount.

Charging plug (left) and ON/OFF/Charge switch (right) mounting
Antenna mounting location. The antenna is a  Linx ANT-916-CW-RCS discussed in this blog.

The original speaker was far too large to provide clearance for the additional battery, DCC-compatible RF receiver, and other electrical components needed for the dead-rail installation. So a 16mm x 35mm speaker was placed in the bottom of the original speaker’s cavity, and UV glue holds the speaker in place.

The original speaker. It is far too large to accommodate the additional dead-rail components: battery, DCC-compatible RF receiver, ON/OFF/Charging switch and charging plug.
Candidate speaker. The actual 16mm x 35mm speaker was even smaller and mounted into the bottom of the original speaker cavity.

Final Demonstration

With the locomotive reassembled, it’s time to test it out! If your locomotive has a smoke unit(s), always ensure sufficient smoke fluid is loaded. Even if you don’t intentionally turn on the smoke unit – sometimes it’s unexpectedly activated.

Initial test run

Common Aspects of 3-Rail to Dead-Rail Conversion of O Scale Steam Locomotives


After doing about eight or so O scale 3-rail to dead-rail conversions for steam locomotives, some similar features pop out that I will discuss in this blog. As with my other O Scale Dead Rail blogs, I will try to stick mostly to my own experience.

A note of caution: O-scale steam locomotives are expensive, and some, to me, are works of art. Consider very carefully whether you have the patience and skill required to make locomotive conversions. I got into O-scale dead-rail conversions to teach myself patience, a few skills, and respect for these beautiful models. Give yourself plenty of time to make these kinds of conversions – being in a hurry is a prescription for trouble – I know because I sometimes got in a hurry. Just don’t.

There are some good tutorials on locomotive repair and disassembly. I recommend this one as a good place to start.

General Considerations

Good grief, what do “general considerations” mean? Well, it’s the general aspects that guide the conversion process for both the locomotive and the tender.

First, most, but not all, of my O scale 3-rail to dead-rail conversion experience is with Sunset 3rd rail steam locomotives: Big Boys, Cab Forwards, Challengers, and Alleghenys, so first off you see that I’m an articulated locomotive fan. Articulated locomotives (AL) can be challenging to disassemble, and, especially, re-assemble. Heck, they are tricky to handle correctly especially since the front driver chassis must in some way “float” to navigate modest-radius curves.

In general, even though 3-rail locomotives pick up AC from the track, the locomotive motors are almost always DC motors, where a connector from the tender supplies the DC power via a connector from the tender. Usually (always in my experience), the two outside rails are electrically connected to the locomotive chassis, and the AC power from the center roller pickups completes the power loop, fully isolated from the locomotive chassis.

These outside/center AC power inputs are typically supplied to the tender from the locomotive via the same connector to provide DC power from the tender back to the locomotive motor. So right off the bat, you have some bad news and some good news:

  • Bad news: We will need to eliminate the physical and electrical connections to the center-rail AC picked up by the center pickup shoes from the locomotive to the tender because we’re not using rail power in dead-rail. This will be accomplished by removing the center rail pickup shoes and, just to be on the safe side, eliminating all of the center-rail AC wiring. In theory, once the pickup shoes are removed, all center-rail AC wiring is isolated electrically, but I don’t take any chances and just remove all of the center-rail AC wiring.
  • The good news about the bad news: We can re-purpose the center-rail AC power plug connection between the locomotive and tender (originally sending center-rail AC power from the locomotive to the tender), and instead we send Switched Battery+ from the tender to the locomotive to provide power to the Constant Voltage Unit that distributes power to components such as smoke units, marker lights, and sometimes the headlamp.
  • Good news: The locomotive’s chassis “ground,” which is electrically connected to the outside rails via the locomotive wheels, does not require electrical connection modification – all we’re going to do is ensure that chassis ground is connected to the tender’s Battery- (Ground) through the original locomotive-to-tender plug. The Battery- (Ground), as the name implies, is also connected to the tender chassis ground.
  • Good news: It’s easy to get the DC power from the tender to the locomotive’s motor(s) through the original locomotive-to-tender plug without modifications to its electrical connections.
Figure 1: Typical locomotive/tender connector pin-out for Samhongsa (Sunset 3rd Rail, Williams) locomotives

Another unique aspect of 3-rail locomotives is the reversing board in the tender that converts the AC power coming from the locomotive to a correctly polarized DC voltage for forward/reverse motion depending on the pattern of interruption of AC to the locomotive. I am not an expert on reversing units – I am in the business of removing them for dead-rail operation. If the locomotive has sound, the sound electronics/card is usually highly integrated (meaning not DCC-compliant) with the reversing unit. So, we must provide a DCC-compliant replacement sound card of a full DCC decoder with sound since the radio-controlled receiver boards “speak” DCC in most cases. Removal of the original sound electronics is a shame because it may have some unique/interesting audio we’d like to reuse. If I ever figure out how to reuse the sound from these original sound units, that will, of course, be another blog. My initial attempts to obtain legacy (remember these cards are sometimes over fifteen years old) circuit interface information from OEM sound card manufacturers such as QSI Industries have not been fruitful, even though they were friendly.

Locomotive Conversion

All of the 3-rail O-scale steam locomotives I have converted to dead-rail had the following aspects of conversion that I discuss in the next three sections: center pickup removal, lighting modifications, and various electrical modifications. Three-rail locomotives are somewhat more challenging than 2-rail to convert because of the unique aspects of power pickup using the third, center rail.

Center Pickup Removal

Removal of the center pickups involves both the rollers themselves and the electrical connections to them. I remove the locomotive pickup rollers because we will usually operate the locomotive on two rails, even though they are unpowered. I suppose you could leave the rollers in place, but this would restrict dead-rail operation to dead 3-rail track. In summary, I think removing the rollers gives you more operating flexibility for dead-rail operation.

See the Figure below for an example of how to remove the undercarriage baseplate so that you can remove the rollers.

Figure 2: Center pickup roller removal

Unfortunately, the undercarriage baseplate requires removal to get to the center pickup roller mounting screw. This plate is usually held in place by six to eight retention screws, but even when you remove them, you have several issues:

  • Often you cannot remove the plate without catching the brake shoes on the drivers. You can solve this problem by removing the brake shoes from one side and sliding the base plate sideways to free to brake shoes on the other side. The wiring underneath the plate connecting to the pickup rollers does not have sufficient slack to allow lifting the cover. You have two options: carefully slip a wire-cutting tool in the narrow space between the freed baseplate and the rest of the chassis, or remove the entire wheel chassis from the boiler section and cut the wires from above. See the Figure below. You still need to remove the baseplate to unscrew the center pickup rollers because you cannot get to them even with the wheel chassis separated from the boiler section.
Figure 3: Center pickup roller wiring modifications. The Constant Voltage Unit is part of an MTH Proto-Sound 3 dead-rail conversion for a Sunset 3rd Rail Allegheny.

Once you free the baseplate from the rest of the chassis, then it’s a snap to unscrew the roller from the baseplate, and cut/remove any connecting wiring. Usually, I also remove the insulator pad screwed into the baseplate.

Once all of this is done, then, of course, you remount the baseplate and any temporarily-removed brake shoes.

Note: Care is required to remove and replace the baseplate. The spring-loaded driver bearings are held in place by the baseplate, imparting significant spring force on the baseplate, which will bend the baseplate unless you uniformly ease in and out the retaining screws. Slight bending is OK but significant, local kinks are bad. Also, these bearings can easily pop out of place, so inspection is required to ensure the bearings are properly seated before tightening down the baseplate.

Lighting Modifications

Steam locomotive lighting includes some or all of the following:

  • Headlamp
  • Marker lights
  • Cabin lights

We’ll discuss each of these in turn


The headlamp is special because we usually want to control its on/off automatically as the locomotive changes direction and possibly according to “Rule 17” which dims the headlamp and tail lamp according to whether the locomotive is stationary (dim) or moving (full brightness).

In my experience with Samhongsa locomotives (Sunset 3rd Rail and Williams), the headlamp is powered by one of two means:

  1. A separate, small rectifying board. It is powered by AC from the center rail and AC from the outside rails and turns on/off power to the headlamp as the locomotive moves forward/backward. This technique is typical of older Williams locomotives.
  2. An output on the Constant Voltage Unit. In this case, you cut the power from the CVU to the headlamp and supply power to the headlamp with a two-wire connector, as described in the previous case. Of course, you should directly trace the wires to the headlamp before you cut any wires. This arrangement is typical of Sunset 3rd Rail locomotives. See the Figure below. When I first started these conversions, I was super-conservative and electrically isolated the CVU from the chassis, and I made a direct, wired connection to the Battery- (ground), as shown in the Figure below. But, using chassis ground, which will be electrically connected to the tender’s Battery- (ground) through the loco to tender plug has worked out OK.
Figure 4b: Modifications to the headlamp electrical connections for Sunset 3rd Rail locomotives. The replacement of the chassis ground by the directly wired connection to the Battery- (ground) is unnecessary. See Figure 4a for more details on how the CVU is connected.

Marker Lights

Marker lights are almost always LEDs whose power is supplied by the Constant Voltage Unit. No modification of the wiring from the CVU to the marker light LEDs is necessary since once you supply power to the CVU, then it will in turn properly supply the marker light LEDs.

Smoke Units

As with the marker lights, once you supply power to the CVU, then the CVU is designed to supply the proper power to the smoke units. A switch is always mounted on either the locomotive or the tender to turn on/off the smoke unit. No smoke wiring modifications are required.

All of the smoke units controlled by CVUs in my experience are Seuthe smoke units, typically requiring 6V DC. They have the disadvantage that they do not “chuff” in coordination with steam locomotives’ piston action. Replacement of these venerable, but unrealistic smoke units with smoke units that contain a “fan” that propels the smoke in synchronization with the sound chuffs from Lionel, ESU, or MTH is a big topic that will be covered in another blog.

An ESU 54678 fan-driven smoke unit that is appropriately sized for O-scale and is designed to work in tandem with ESU LokSound decoders such as the LokSound L.
An ESU 54678 smoke unit with additional brass tubing is to be installed in a Williams UP Challenger
A preliminary position install of an ESU 54678 smoke unit in a Williams UP Challenger to determine if the ESU LockSound L V4.0 decoder would fit behind the smoke unit. This smoke unit has two connections each for the heater, fan motor, and thermistor. The thermistor provides a temperature measurement of the heater to the LokSound L’s sensing circuitry that will carefully control the temperature.
Detail of the Williams UP Challenger smoke stack with smoke unit tubing. The original Seuthe smoke units were cut to retain only the funnel that fits over the smoke unit’s brass tubing. Care is taken to ensure the smoke fluid is inserted directly into the brass tubing.
A Lionel 610-8057-200 fan-driven smoke unit I have used for O-scale installations.

The smoke unit pictured below is very similar to the Lionel 610-8057-200 smoke unit pictured above. It was retrofitted with a 100K thermistor to emulate the ESU smoke unit inputs for a LokSound L V4.0 decoder.

This smoke unit is almost identical to the Lionel 610-8057-200 with modifications. All of the original electrical components have been removed, and a connecting trace was cut to isolate the Heater Resistor +/- from the Fan Motor +/-. Liquid tape was applied to the smoke funnel lip to enhance mounting friction and improve sealing. A 100K thermistor was installed adjacent to the 27 ohm heating element to emulate the ESU smoke unit inputs to a LokSound L V4.0 decoder.
This smoke unit is almost identical to the Lionel 610-8057-200 unit installed in a Sunset 3rd Rail Allegheny with a custom brass mounting bracket.
An MTH AA-0000070 fan-driven smoke unit that is well-sized for O-scale.
The MTH AA-0000070 smoke unit pictured above with custom brass brackets for mounting in a Sunset 3rd Rail AC-6 Cab Forward. The small size of this smoke unit is well-suited to the tight fit afforded by this locomotive. This smoke unit has no thermistor, so it easily interfaced with the Zimo MX-969KS decoder installed behind the smoke unit. This decoder is ideal for O-scale installs because of its narrow form factor.
A Zimo MS696KS DCC decoder and screw-terminal board. The decoder’s slim design and well-documented connections for fan-driven smoke units make it a good choice for O-scale installs. “Ventilator” (which turns on/off 5V to the motor) and Ground are used to turn on/off the smoke unit’s fan, and +Power and any of the Zimo’s “FA” connections, which are software-controlled switches to open/close a connection to ground, controls turning off/on the smoke unit’s heating element.

A final note of caution on smoke units: When using smoke units with metal cases, it’s crucial to ensure that the heater element (resistor), fan motor, and thermistor (if there is one) are completely electrically isolated from the metal casing that will be in firm contact with the locomotive ground. You should verify this with an ohmmeter. If you don’t check each lead to verify there is no electrical short to the smoke unit case, you will be sorry. I have forgotten twice (I learn slowly sometimes) to check for electrical isolation of these components from the smoke unit case, and I poured amps from a battery in the tender to the locomotive along a direct path from Battery + to Battery – (ground), melting lots of wiring along the way. This error will cost you hours of work and possibly dozens to hundreds of dollars in damaged electronics.

Original Equipment Manufacturers (OEMs) often made a point of ensuring good ground contact with some of the smoke unit components – we don’t want this. We want the decoder (or the RF receiver if it’s handling smoke unit control) to handle how these components are electrically routed to the ground! Yes, these components all need power which we frequently supply from a common source, but it’s the route to ground that we want to control carefully.

As a side note, pay careful attention to the voltage requirements of the smoke unit components. Different voltages almost always supply the heating element and motor! I have never seen a smoke unit motor that didn’t require 5 Volts. I have inadvertently killed one of these cute little motors by accidentally supplying it with 14.8V.

The heating element’s voltage depends very much on its resistance (they vary from 6 ohms to 28 ohms) and interaction with the electronics that control it, such as a DCC decoder or an Airwire RF receiver such as the G3. You need to carefully understand the specs of the heating element and the device that will control it. Spend some time reading. As a general rule, you tend to stay out of trouble with higher resistance heating elements because, for a fixed supply voltage, the power produced by the heating element is inversely proportional to the resistance (remember: Power = (V*V)/R, where power is in Watts, V is in Volts, and R is in Ohms).

Even if you are within the proper voltage supply range for a smoke unit, you can still burn them up under certain circumstances. Pay heed to the dark warnings that you should always run your smoke unit loaded with the proper amount of smoke fluid. As the fluid evaporates, it cools the heating element – no fluid and the heating element and the specialized batting that wicks the smoke fluid into contact with the heating element will get hotter. Often, it’s the wick that gets scorched with too high temperatures or no smoke fluid, and this scorching damages the wicking action.

Example of a fan-driven smoke unit’s wick (in the left chamber)

That’s why some smoke unit manufacturers, such as ESU, use thermistors to measure the heating element’s temperature and send this information to the decoder so that it, in turn, can adjust the voltage to the heating element to prevent burn-up. So far as I know, only ESU DCC decoders have thermistor inputs for this smoke unit feedback control. I have reverse-engineered an ESU smoke unit and found that it uses a 100K thermistor that can be easily purchased and retrofitted into other smoke units if you intend to use the smoke unit with ESU decoders. High-melting point solder must be used when adding a thermistor. Lacking that decoder feedback control of the smoke unit’s heater, I have devised a compact temperature feedback control, but that’s for another blog…

Lionel fan-driven smoke unit with a thermistor retro-fit for use with a LokSound L V4.0 DCC decoder. High melting point (HMP) solder should be used when soldering thermistors or replacement resistors on smoke units. (Note the munged “Lionel” name on the board. It’s a genuine Lionel board, but I doubt it was “MadoinUOA”.)

Electrical Modifications

Constant Voltage Unit

We have already discussed the Constant Voltage Unit (CVU) a bit under the section dealing with headlamp modifications. Some locomotives have a Constant Voltage Unit (CVU) that converts AC power from the outside rails/chassis (ground) via the locomotive wheels and center-rail AC via the center pickup shoes, respectively, to a constant voltage for components such as smoke units, LED marker lights, and cabin lights. The CVU usually consists of a rectifier to convert AC to DC, a capacitor to “smooth” the DC, and a voltage regulator to maintain the output DC at a constant voltage, frequently six volts as required for Seuthe smoke units used by Samhongsa-manufactured locomotives (Sunset 3rd Rail and Williams locomotives).

I have encountered three types of CVUs:

  1. MTH Proto-Sound 2/3 versions that power maker light LEDs and incandescent cabin lights (see my blog on dead-rail conversion of a Proto-Sound 3.0 locomotive).
  2. Sunset 3rd Rail CVUs that are usually mounted at the front of the boiler and power Seuthe smoke units and marker light LEDs.
  3. Williams CVUs are similar to Sunset 3rd Rail CVUs but do not control the headlamp, and instead use a separate Headlamp Direction Board.
Figure 5a: Proto-Sound 3.o Constant Voltage Unit in a Sunset 3rd Rail Allegheny converted to dead-rail. “Switched Battery B-” is also ground.
Figure 5b: Typical Sunset 3rd Rail Constant Voltage Unit with dead-rail modifications. See Figure 4a for details on how the CVU is connected to power.
Figure 5c: Typical Williams Constant Voltage Unit with dead-rail modifications. See Figure 4a for more details.

Important Constant Voltage Unit Control Options: In the figures and discussion above, I modified the Constant Voltage Unit power supply to connect to Switched Battery+ and Battery- (ground) from the tender. These connections will always turn on the devices supplied by the CVU (although the locomotive-mounted smoke switch will turn on/off the smoke unit) when you switch on the battery in the tender. To allow the receiver to control the CVU-connected devices actively, you can replace the Switched Battery+ input to the tender-to-locomotive connector with a relay, controlled by the receiver, that turns on/off Battery+ to the CVU. See the Figure below for an example. You mount this relay in the tender, not the locomotive!

Figure 6: Tender relay control of Switched Battery+ supplied to the locomotive CVU. The relay is “normally-open”.

In this example, a 215H-1CH-FC12VDC relay, with a 1N4002RLG protection diode in parallel across the input control (these parts are available from by cutting and pasting the above part #’s into their search), will connect/disconnect Switched Battery+ to the locomotive’s CVU according to whether the Airwire G3’s RM1-8 output is on (shorted) or off (open-circuit). Unpowered (i.e., RM1-8 is off), the relay is “normally open”, so no power reaches the CVU from the relay. When the relay is activated (i.e, when the RM1-8 is on), the relay closes to supply Switched Battery+ to the CVU. Setting up the on/off logic for the Airwire G3’s RM1-8 output by remote control is described here, recognizing there are slight differences between the device part numbers and wiring hook-up described in the link and those presented here. It’s kind of neat to hear the mechanical relay quietly click closed and open…

Of course, there are numerous other techniques for implementing a high-amperage switch that is controlled by the receiver or DCC decoder. This particular example is called a “high-side” switch that connects/disconnects battery power to the device, as contrasted with a “low-side switch” where the device’s connection to ground is controlled by the switch.

Locomotive to Tender Connector

Tender Conversion

Good news: tender conversion is usually much easier and less diverse than the modifications needed for dead-rail conversion of locomotives.

Reverser Unit Removal

Sadly, the sophisticated electronics contained in the tender must be removed almost totally, including the reverser unit. These electronics are not to be confused with a possible MTH PS-2 or PS-3 controller that you probably want to keep as described in another of my blogs.

Reverser-sound electronics from a Sunset 3rd Rail UP Big Boy tender.

As I have mentioned in other blogs, it’s a shame that you cannot reuse some of the electronics containing the sound data, but I have not discovered a way to do this. (I still have hope of someday figuring it out, so I have kept and labeled all of the electronics I have removed – you should, too.)

I strongly urge you to take pictures of the tender assembly and its electronics before the removal or modification of any components – you might be glad you did. Document everything with a picture – that’s what cell phone cameras are for!

The board removal process first consists of carefully disconnecting any wiring to the boards (with pictures and notes!). Usually, plugs provide these connections, but occasionally, clipping off the wiring becomes necessary. I would suggest that you leave enough wire connected to the board to facilitate a new wiring connection just in case you reuse or sell the boards.

Wire removal may entail plug removal and wire cutting.

Some of the wiring such as to tender lights and connections to the locomotive needs to be carefully preserved.

After wire removal, then the boards can usually be separated from the tender by removing mounting screws or two-sided tape.

Board removal for a Sunset 3rd Rail Cab Forward tender.
Care must be taken to separate the battery from the double-sided tape and then remove the tape from the tender.

Battery Addition

As I have mentioned in other posts, I mount the batteries for O-scale steam locomotives in the tender. For 14.8V operation, I use 4 LiPo cells in series (the so-called “4S1P” configuration). Regardless of how you ultimately arrange the individual 3.7V LiPo cells relative to each other, you can’t get around the fundamental size limitations imposed by a single LiPo cell on O-scale: the cell’s length. Generally, O-scale tenders are not wide enough or tall enough internally to provide sufficient clearance for even a single LiPo cell aligned along the width or height of the tender. So, this almost always means orienting the cells lengthwise in the tender in some fashion.

Even knowing this constraint, fitting a 4S1P battery pack into the tender sometimes requires a bit of ingenuity/trial-and-error. There are no hard-and-fast rules here, so I will provide a series of figures showing how I’ve “done it.”

Some suggestions:

  • Use thin Velcro tape to mount the battery to the tender frame, usually on the chassis, not the tender hull. I mount the “hooks” side of the Velcro to the frame and the “loops” side to the battery – I suppose this is an aesthetic choice, but I believe consistency is good: so my rule is all Velcro on the frame are “hooks,” and all things that are mounted using Velcro “loops.” See the picture below for the kind of Velcro I use.
Thin, industrial strength Velcro useful mounting items inside the tender and locomotive.
  • Use three position, ON-OFF-ON switches when connecting the battery “+” side (the battery “-” should be well-connected to “ground”, which should include the tender and locomotive frames):
    1. ON: power supply for all items on the tender and locomotive
    2. OFF: “neutral” that completely disconnects the battery to prevent slow discharge when not in use
    3. ON: recharging jack
    • Use high-quality switches and recharging jacks. Cheap ones available on Amazon are generally foreign-made junk. Spend two or three dollars apiece and purchase them from reputable electronics distributors such as Mouser and Digi-Key. I have been sorry when I used cheap hardware.
    Example battery, switch, and charging plug mounting where this is plenty of room. Note the shielded antenna connection from the chassis to the Airwire receiver mounted on the side of the tender hull. Velcro is used to attach various electrical components, including Wago connectors that supply Battery + and Battery – (ground) to other electrical components.

    An example (on a Sunset 3rd Rail Cab Forward) where the battery must be mounted to the tender hull since the battery pack is just slightly too wide for the tender hull opening without scrubbing.

     Antenna Mounting

    Placing an antenna and external electrical connections is never an ideal process: compromises must be made that try to minimize the impact on aesthetics and maximize RF reception and accessibility.

    While far from ideal, I frequently place the antenna in the dark reaches under the tender chassis. The RF engineers are going to jump all over me for doing so because there’s a lot of metal in a nearby plane parallel to the antenna axis – the location “works,” but the reception range takes a hit. The Figure below is a typical example of mounting for the antenna, an electrical switch, and a charging plug.

    Example (in a Cab Forward) of antenna, power switch, and charging plug location on the bottom of the tender. The fit is tight!

    Sometimes, when the tender has a coal load, the antenna can be hidden underneath a “coal cloth” on the top of the tender. This strategy sometimes improves reception when there is an opening beneath the coal load where you can place the antenna. Frequently the original coal “load” is either mounted with screws (if you look carefully) or is easily pried off with the mounting board. See Figure below.

    Example of coal “load” removal on a KTM Big Boy. Underneath is a cavity that is suitable for mounting an antenna

    At the risk of offending some purists, sometimes an opening can be cut in the tender hull where the coal load goes to afford both better antenna placement and internal access to the electronics in the tender. The opening will be covered over by the coal cloth. See the Figure below for an example of this strategy.

    Example (Sunset 3rd Rail Big Boy) of an opening cut in the tender hull to provide antenna placement and electronics access. Note the “coal cloth”, which is non-metallic, over the opening to provide low-loss RF reception.
    Top view of the flexible “coal cloth” placed over the opening cut in the tender hull for antenna placement and electronics access.
    The coal cloth in the previous figure has been removed to reveal the open-cavity antenna installation in a Williams UP Challenger. The antenna is connected to a Tam Valley DRS-1, Mark III, RF receiver that operates on Airwire Channel 16. The nearly half-wave antenna provides better range performance compared to tender undercarriage installations shown in this blog.

    Antennas themselves involve some compromise because they must be short to fit within the confines of our locomotive or tender or in the area around them. Very generally speaking, shorter antennas are less efficient than longer ones. Most dead-rail transmitters/receivers operate (in the US) in the band ranging from 902 MHz to 928 MHz, which is one of the so-called “ISM” (Industrial, Scientific, and Medical) bands that does not require strict licensing to use. This frequency converts to wavelength in vacuum is about 33cm, which at even “quarter-wave” makes for an antenna of roughly 8.25 cm or about 3.2 in unless, for instance, you reduce the length by making the embedded antenna wire helical.

    Compact, high-quality, quarter-wave 915 MHz ISM antennas are manufactured by reputable vendors such as Linx Technologies in convenient right-angle form-factors with RP-SMA connectors (see Figure below) and are available at Mouser or Digi-Key. Again, my suggestion is not to purchase cheap antennas of unknown quality: when range performance is poor it will be very difficult to know what to blame. Just don’t worry about the antenna and buy quality: it’s only going to cost you seven to 11 dollars US.

    A Linx ANT-916-CW-RCS antenna. It’s about 2.1 inches long. This antenna uses a helical internal antenna wire to reduce its length.

    Receiver Addition

    Because this topic is not unique to 3-rail, please see this post for a discussion of Transmitter/Receiver Addition.

    Lighting Modifications

    Three-rail locomotives have a variety of means for providing two aspects of lighting: constant output with changes in track voltage, and whether to turn on or off with direction or independent of direction, especially since AC operation makes it more challenging to determine direction.

    We have already talked a bit about the role of constant voltage units (CVUs) for lights in the locomotive, and tenders often have colored marker lights and almost always have a white tail light. AC voltage from the rails usually powers these lights, so almost all of the electrical “infrastructure” used to supply AC lighting power must be replaced for battery-powered DC operation.

    These lights are often older incandescent bulbs that are more power-hungry than LEDs. Since dead-rail conversion involves the use of DC battery power of around 14.8V or so, LEDs with the proper form factor and protection resistor to replace these incandescent bulbs are easy to find for colored marker lights or the rear light. The figures below are an example of LED installation in marker lights and tail lights.

    Details of marker light and rear light LED installation. Note that there are two rear lights using heavier wiring. UV curing “glue” is used to hold the wiring and LEDs in place. This type of glue provides reasonable holding ability but can be easily removed if necessary. It has the added benefit that it will not harden until UV light is applied, giving the user plenty of time to carefully position the wiring and glue.
    Sunset 3rd Rail Big Boy LED marker light and rear light conversion (there are two rear lights in this case). Note the use of “canopy glue” to hold the LED in place and provide a “window”. When the canopy glue cures, it will be transparent. The LED lead wires were later painted black to reduce their visibility.

    If the original marker or tail lights are LEDs, then retaining most of the wiring supplying power is desirable. The wiring to the LEDs must be cut somewhere to convert to battery-powered operation, but look carefully for the protection resistor in series with one of the power leads to the LED, and do NOT cut the wiring between this resistor and the LED. As a side note, if you connect power directly to an LED without a protection resistor in series with the LED: if the power supply “forward biases” the LED, you will burn it out with too much current – a brief, tiny nova will ensue. Frequently, the protection resistor is near a plug, making it convenient to retain this plug.

    For 14.8V operation, the LEDs I have used require protection resistors ranging from 470 ohms to 1.2 Kohm. The specific value is dependent on the LED: smaller LEDs generally tolerate smaller maximum currents, so larger protection resistances are required.

    LEDs produce light only if you apply a positive voltage to its “anode” relative to its “cathode.” It’s the electrical equivalent of a stop valve. In essence, current flows easily through a diode in only one direction, so even in the original wiring, either a positive DC or positive rectified AC voltage supplies the LED anodes.

    Ensure that the original DC or rectified AC voltages are reasonably close to the replacement battery voltage so that you do not need to modify the resistance of the protection resistor. Make sure that the replacement power connects with the same polarity as the original power supplied to the LED. If powered “backward” for very long, damage to the LED may result. Brief reverse biasing with the protection resistor in series with the LED to test for the proper polarity is not harmful, just don’t apply it for long. The 14.8V batteries I use are generally not vastly different from the original voltages supplied to the LEDs, so increasing the protection resistance is usually not necessary.

    After connecting the LED to battery power, if the LED seems too bright, by all means, add a resistor in series with the LED and the original resistor to reduce the current through the LED. A higher-than-necessary value for the total series resistance will not cause problems, and frequently LEDs are just too darn bright using the “proper” value for the protection resistor.

    Mechanical Modifications

    Caution: This topic is somewhat controversial. Some may not like the suggestions under this topic. Please try to remember that the discussion is only offering possibilities, not hard-and-fast rules.

    The most important mechanical modifications to 3-rail locomotives deal with the “high-rail” flanges on all of the wheels. If you intend to use high-rail trackage, then the discussion below is probably irrelevant.

    However, if you, like me, dislike the very non-prototypical appearance of the high rail trackage and the large wheel flanges that go along with this kind of trackage, or if you want to operate on 2-rail track that conforms to the “Scale Track, Standard Scale” NMRA Standard S-3.2, then the high-rail flange profile requires modification to better match “Scale Wheels” in NMRA Standard S-4.2 and “Wheel Contour” NMRA Recommended Practice RP-25.

    There are no doubt numerous strategies for replacing high-rail flanges, and I’m sure I haven’t thought of them all. The two approaches I will discuss are wheel replacement or flange profile modification.

    A final note of caution before describing details: Please determine how you will use your dead-rail locomotive. If you will be using the locomotive strictly on un-powered rails, as I do, then proper wheel insulation is not an issue.

    However, if you intend to run your locomotive on powered trackage, then proper wheel insulation may be required. If the powered trackage is 3-rail, then insulation is not an issue since the wheels are by design uninsulated. However, if the trackage is powered 2-rail, then proper wheel insulation is required. Operating 3-rail locomotives on powered 2-rail requires wheel insulation, which is a major hassle, especially when dealing with locomotive drivers.

    The powered 2-rail standard is that the locomotive frame is electrically connected to the right rail, so all of the locomotive’s left wheels must be insulated; and the tender’s frame is electrically connected to the left rail, so all of the tender’s right wheels must be insulated.

    My suggestion: don’t operate dead-rail O scale locomotives on powered trackage at all, but most notably not powered 2-rail trackage. But, this may not be an option for you, so you must address proper wheel insulation for powered 2-rail operation, and you must ensure the locomotive and tender frame do NOT share a common ground. Otherwise, a short across the two rails will occur.

    Wheel Replacement

    Wheel replacement may involve completely replacing the high-profile wheel with an RP-25 conformant wheel, or, in the case of steam locomotive drives, replacement of the outer rim or “tire.” We will discuss each in turn.

    Complete wheel replacement is a very feasible option for leading/trailing locomotive trucks and tender wheels. Specialty vendors such as Northwest Short Line (NWSL) and Precision Scale offer numerous sizes and styles of RP-25 compatible wheels and axles. I will warn you that navigation of these companies’ offerings is either fun or tedious, depending on your level of desperation and patience. While looking for what you need, remember that this is supposed to be a fun hobby.

    The knottiest problem with wheel replacement is dealing with the axles. You can completely replace the wheel axles along with the wheel replacement, or you can bore out the replacement wheels’ inner diameter to match the original axle’s diameter.

    For instance, NWSL almost entirely offers both replacement wheels with an inner diameter of 1/8″ for O scale and axles that match this diameter. High-profile wheel axles are almost always a larger diameter. If you can find a 1/8″ axle that matches the length and end-style of the original axle, by all means, go with this option.

    Unfortunately, you may not always find a suitable axle. If you are handy with a lathe, then making a new 1/8″ diameter axle that matches the original axle’s length and end style will be a fun project. If machining is not your forte, then you might try boring out the replacement wheel to match the original axle’s diameter.

    I will warn you, however, that boring and mounting the replacement wheel on the original axle is somewhat challenging, and requires the right tools, technique, and skill.

    As a final note on wheel replacement, ensure that if you intend to operate your locomotive on powered 2-rail trackage (which I don’t recommend), then proper wheel insulation is required. The vendors above offer insulation options along with replacement wheels and axles.

    Flange Profile Modification

    The NMRA Recommended Practice RP-25 and NMRA Standard S-4.2 help define the wheel flange profile that will operate reliably on two-rail trackage meeting the NMRA Standard S-3.2. These wheel profile and trackage standards are more prototypical-looking than high-profile flanges and track, and RP-25 profile wheels will work on high-profile rail if it’s well laid, but high-profile wheels will not operate reliably on NMRA Standard S-3.2 compliant turn-outs.

    RP-25-compliant replacement steam locomotive drivers are generally not available, so modification of the original drivers is usually required.

    In some cases, it is possible to remove the driver center from the “tire.” Then an RP-25-compliant tire is machined and press-fit onto the driver center. Some modelers, such as Joe Foehrkolb and Glenn Guerra excel at this process, but I don’t, so my alternative is to machine the tire while still integrated with the center driver until its flange profile approximates the flange depth (approx 0.036″) and flange width (0.039″) dimensions of an RP-25 profile.

    The following photos demonstrate my process. Of note is that the most critical dimension to “get right” is the flange depth, which means reducing the flange diameter with a series of small “side-cuts” (parallel to the lathe spin axis) on a lathe until the flange diameter is about 0.072″ larger than the “tire” diameter. Then a series of small face-cuts (radial to the lathe spin axis) reduces the flange width until it is approximately 0.039″. However, this dimension is less critical than the flange diameter, so the flange width should not be reduced by so much that it leaves a sharp flange edge.

    Step 1: removal of the side-rods
    Step 2: Removal of the driver axle coves
    Step 2: Sometimes you must use a specialized “wheel puller” to pull the drivers off the axle that is mounted inside a solid, bored chassis
    Step 3: Machining the drivers: The tail stock holds the axle steady and square. A series of small side-cuts (parallel to the lathe spin axis) with a right-handed cutting tool decreases the flange diameter until it is approximately 0.072″ greater than the driver diameter to create a flange depth of approximately 0.036″. Then a series of small face-cuts (radial to the lathe spin axis) with a left-handed tool reduces the flange thickness to approximately 0.039″. This dimension is less critical than diameter reduction, so residual flange appearance is an important concern.
    Final driver: the flange depth is approximately 0.036″ and its width is approximately 0.039″.
    Example of high-profile flange reduction for both the drivers and truck wheels.

    Dead-Rail Conversion of a Sunset 3rd Rail Allegheny 2-6-6-6 Locomotive with MTH Proto-Sound 3


    Please don’t jump to conclusions; MTH did NOT manufacture the C&O 2-6-6-6 Allegheny with MTH Proto-Sound 2.0 (PS2.0) I found on eBay. Instead, it’s a brass locomotive produced by Sunset 3rd Rail (Figure 1) and converted to PS2.0 (see MTH PS2.0 Upgrade Manual). See Figure 2. The retrofit replaced the original tender QSI-OEM Digital Soundboards, the wiring harnesses for the tender and locomotive, and the Suethe smoke units and their voltage regulator board in the locomotive.

    Figure 1: Sunset 3rd Rail C&O Allegheny box info


    Figure 2: Original tender Proto-Sound 2.0 electronics and harness wiring

    It was a well-done conversion, so I was very reluctant to tear out the tender PS2.0 control board and the wiring harnesses in the tender and locomotive. The PS2.0 conversion used an MTH smoke unit with fan speed and smoke intensity controls.

    Figure 3: MTH Smoke Unit with funnel

    The CVP Airwire receiver boards I typically use for dead-rail conversion don’t have this level of smoke unit control. And the PS2.0 board used a speed encoder on the locomotive motor’s flywheel to synchronize the PS2.0 board’s sound. See Figure 5 for the speed encoder reader and flywheel strip and 5b for additional electrical connections.

    Figure 4: Original Constant Voltage Unit wiring with dead-rail modifications indicated


    Figure 5: Speed encoder, flywheel strip, and electrical connections for the Constant Voltage Unit.


    Figure 5b: Locomotive harness wiring after modifications connecting the Constant Voltage Source to Battery +/- and replacing incandescent bulbs with LEDs

    These built-in features were excellent, but I still wanted a dead-rail conversion.

    Hmm… Looking around, I discovered that Proto-Sound 3.0 (PS3.0) had DCC/DCS control options, and the wiring harnesses are the same for PS2.0 and PS3.0 boards (see, for instance, MTH PS3.0 Upgrade Manual). Things are looking up. Then I found a great site, Ray’s Electric Trainworks, that provides PS3.0 replacement boards and great support.

    My thought was this: if I can upgrade the locomotive to PS3.0, then I can take the following steps. Jumper the PS3.0 board to DCC operation, disconnect the original rail power/communication wiring, and re-connect the rail power/communication wiring to the DCC outputs of a CVP Airwire CONVRTR-60X receiver (CONVRTR Users Guide). Easy, right? Not so fast.

    Ray at Ray’s Electric Trainworks was a great help: he steered me to the right PS3.0 card I needed for the tender and loaded the Allegheny sound file for me. Otherwise, I would need a bunch of DCS infrastructure to load the sound file. And he gave me a rebate for the old PS2.0 card! Great guy.

    OK, I have the PS3.0 card from Ray. The PS3.0 card came mounted in its plastic carriage that is screw-mounts on the tender chassis through pre-existing holes. The heatsink orients a bit differently between the PS2.0 and PS3.0 – no big deal – I just needed to drill a hole in the tender chassis in a slightly different place. The PS3.0 doesn’t use a Ni-MH battery, so out it went. That was a good thing, too, since I needed the real estate for the replacement LiPO battery to supply power to the control boards, lights, smoke unit, and locomotive.

    Locomotive Modifications

    Here is a diagram of the locomotive wiring harness from the MTH PS3.0 Upgrade Manual with my annotations.

    Figure 6: Locomotive PS3.0 wiring harness with modifications indicated

    Since I wouldn’t send track power to the tender, I cut the Ground Lead and Pickup Roller Leads wires. I re-purposed them by connecting these harness wires to the Constant Voltage Unit, a heat-shrink blob whose input leads were cut from their original chassis connections (see Figure 5 again).

    While I was at it, I removed the incandescent cabin and headlight bulbs to reduce power consumption. I replaced them with Yeloglo LEDs (see Yeloglo description), whose + input was in series with the Yeloglo’s 470-ohm resistor for 10-16 Volt operation. Yeloglo LEDs have an excellent yellowish output reminiscent of incandescent light.

    Tender Modifications

    The diagram below shows the tender’s wiring harness with my modifications.

    Figure 7: Tender PS3.0 wiring harness with modifications indicated

    Continuity testing revealed that the locomotive Roller Pickup Leads and the Ground Lead connected to Pin 1 and 3 of the 7-pin connector, respectively.

    Note that BOTH locomotive and tender Ground Leads (both are black) that are input to the PS3.0 on pins 3 and 4 of the 7-pin connector, respectively, MUST BE DISCONNECTED FROM THE LOCO/TENDER FRAMES AND CONNECTED to the “B” DCC output of the CONVRTR. This pair of connections was the trick. I initially connected ONLY the Ground Lead from the locomotive (pin 3 of the 7-pin connector) to the CONVRTR, which did NOT work! I don’t know if only connecting pin 4 of the 7-pin connector would work – I didn’t try it.

    Similarly, I disconnected the red wire that is input to the PS3.0 on pin 1 of the 7-pin connector (which initially connected to the locomotive Roller Pickup Leads) from the plug bundle that connects the tender to the locomotive. I connected it to the “A” output of the CONVRTR.

    The “harness side” of the two cut wires originally going to the Pickup Roller Leads (red) and Ground Lead (black) on the locomotive were connected to switched Battery + and Battery – (ground), respectively, to provide power to the locomotive’s Constant Power Unit.

    Note: “Switched B+” means battery power coming from the Battery’s + terminal that is turned on or off with a switch (you want to be able to turn off the power!). “Battery – (ground)” means the connection to the Battery’s negative terminal that is usually grounded to the tender chassis by a battery charging plug.

    A picture is worth a thousand words, so studying Figures 6 and 7 will tell you what wiring cuts and re-connections are needed to convert a Proto-Sound 3.0 steam locomotive to dead-rail.

    Other Dead-Rail Conversion Details

    Of course, other aspects of the dead-rail conversion are required. These aspects include adding battery power and CONVRTR connections and removing center-rail pick-ups and electrical connections that are part of a typical 3-rail to dead-rail conversion for an O-scale steam locomotive. These conversion aspects are discussed in another blog.


    In summary, if you have a locomotive with the PS3.0 installed, conversion to battery-powered DCC operation and radio control (dead-rail) is straightforward once you know the few wiring cuts and re-connections you need to make. The DCC operations for this particular locomotive can be found in the MTH document “Premier 2-6-6-6 Allegheny Steam Engine .” What you preserve with the PS3.0 is good DCC functionality, the original sound, and coordinated smoke – and that’s a pretty nice combination.