I had a similar problem installing a Digitrax decoder in a Doodlebug. When I removed the old jumper plug from the PC board socket, the guts from the #1 socket connector came out with the plug. Seems like the person that prepared the socket got a little too close to the connector with the cutoff wheel and damaged it. 
In my case it was the orange motor lead that was open. I could get lights but the Doodlebug would not move. Now, if a similar thing happened to your #4 or #8 (Red or Black track power circuits) you would get no track power to your decoder. But, the decoder would work fine in another locomotive as mine did.
I removed the old 8-pin socket and replaced it with one that was carefully cut from the stock strip. Why didn't I just solder direct? I have an additional function only decoder in the Doodlebug for the passenger compartment illumination. The plug and socket connection facillitates making changes and programming. The motor decoder and the function decoder have the same address and you don't want to program them at the same time.
In my case it was the orange motor lead that was open. I could get lights but the Doodlebug would not move. Now, if a similar thing happened to your #4 or #8 (Red or Black track power circuits) you would get no track power to your decoder. But, the decoder would work fine in another locomotive as mine did.
I removed the old 8-pin socket and replaced it with one that was carefully cut from the stock strip. Why didn't I just solder direct? I have an additional function only decoder in the Doodlebug for the passenger compartment illumination. The plug and socket connection facillitates making changes and programming. The motor decoder and the function decoder have the same address and you don't want to program them at the same time.
That's what you call creepy 