Make sure the backup light wires aren't shorted or they'll cook the FET on the control board. You can add a backup light by just supplying a 6V bulb and drilling out the dummy backup light if it exists, or adding the backup light fixture if it doesn't.
With the PCB in the locomotive, the volume pot leads are still brought back to the tender, so you can still control the volume from the tender.
Wire one end of the pot to the wire from the tether pin-3, wire the wiper of the pot to pin-7, and wire the other end of the pot to pin-5. Obviously, all of these wires should be available at the end of the tether cable.
