I just bought a used Shay. It’s from the second run with six screws on the bottom plate. I bought some replacement metal trucks. The instructions mention red and black wires. When I took the old trucks loose I found two black, one red and one white wire. Is this another version or could the previous owner have done some modification when he added a sound system?
Typical Bachmann wiring, you will have to sort out the wire polarity using the front and back lights.
Check out George’s sight, look under tips, Bachmann Shay truck replacement
http://www.girr.org/girr/index.html
Good luck
Rick