to Brian and Loco Bill,

Thank you for your help! i was able to decifer the color coding of the wiring for this old r/c model 90-0100-27. the sound really is the chuff switch grounding through the axle pick-ups.
if anyone needs a schematic of this model i will post it upon request.

thanks loco bill,
the engine has been disassemble and the only thing left is rewiring the new pcb with the right color wires. the only wires that were still attached to the board were the brown and the white (speaker) i still have the red and black(power from the batteries) and a green and yellow. i assume the last two are sound but not sure.

can anyone supply me with the wiring color code to the small printed circuit board where the power on-off,sound on-off switches and the speaker output plug are mounted near the boiler on a 90-0100-27 r/c engine. the original pcb board was damaged by battery acid along w/ the wiring. a new board has been etched.