I just picked up a Williams E7 Dummy B at a train meet. I got it for parts as it had a short in it. The unit has been upgraded to TMCC with Railsounds and Williams Power Trucks. I fix a few problems and everything works fine including the TMCC and Railsounds with the exception of one Power Truck where if you move the truck little, it shorts out (not in the same spot sparks jump from the truck to the frame).

I have a lot of experience fixing trains however none in Williams and looked for the obvious of what could cause the short but couldn't find it. With everything else working fine I don't want to take a chance now, so I was hoping someone could point me in what to look for next. I'd like to remove the truck and test it on my bench away from the TMCC components but I am not sure how to remove the truck. Also do Williams Power Truck motors run on AC or DC for testing on my work bench?

Any help would be greatly appreciated.