Hi Vic58
I think you are referring to the Great Northern 4-8-4 steam loco #6-3100. I suggest you add the engine number in the title of your post since many of us own the engine and may be able to help. I own this engine and love it. The sound boards fail, mainly due to the foam that it sits on in the tender breaking down over time such that it eventually touches the metal frame and goes kaput. Its an easy fix, but owners need to check the foam before starting up the engine.
I have also added the service document, in case you need it. Below is the diagram from the Lionel service supplements 1-47. There are some rudimentary wiring drawings. Hopefully, someone will chime in with more direct help.
