Sounds like a grounding issue - just spit balling here. Take the headlight wire out of the equation, take it loose and just tape over it, then rehook the power pickup wire back to the positive brush - the loco should run. These things are pretty simple as far as wiring goes. So long as you've got a hot brush and a grounded brush, the thing has to run as long as the laws of physics are still in play. However, if the armature's blown or there's a faulty reverse mechanism involved, all bets are off! Good luck!
