1) Remove locomotive shell following Roundhouse instructions.
2) There are two large diodes, one on each side of the rectangular light board. Remove them.
3) The two LEDs are wired to this light board, one on each side with black and gray wires on each LED. Reverse the black and gray wires on the board from each LED (gray to where black was and black to where gray was.
4) Remove the dummy eight pin plug and insert the eight pin DCC medium plug of a Digitrax DZ1xxPS decoder with the orange wire going to #1 on the light board.
5) Reinstall locomotive shell.
FAILURE TO FOLLOW THE ABOVE STEPS CAN RESULT IN DAMAGE TO YOUR DECODER AND/OR LIGHTS NOT WORKING ON THIS LOCOMOTIVE.
It should also be noted that many operators have chosen to hard wire the decoder in the Model 40 rather than rely on the 8-pin plug.