I purchased this completely scratch-built item circa Dec 2020 from a private seller.
The decoder is a Titan Large Scale decoder. Documentation can be found in the Installation Manual and Wiring Diagram. Check this website for further documentation.
Currently, the locomotive operates by receiving wireless DCC from an Airwire transmitter, NCE Gwire transmitter, or a ProMini Air transmitter on Airwire channel 0 at DCC address 3 (see demo move above). The locomotive will ignore track-based DCC signals in this “mode” of operation. The Installation Manual shows how to change to track-based DCC operation using CV re-programming in either PROGRAM or OPS mode. Note that the switches on the bottom of the tender must be set to “TRK” as well.
Using a wireless throttle such as the CVP Airwire T5000 or the ProMini Air transmitter connected to a standard DCC throttle, I changed to track-powered operation by putting the throttle into “OPS” mode, setting CV46 to 1, and then setting CV56 to 0. Then turn the battery off in the battery car (or simply disconnect the battery power plug going from the battery car to the tender), and set the two tender switches to the “TRK” setting. Then apply either DCC or DC track power and away you go!