Lionel MPC J 611 Upgraded to TMCC

The obvious things are to check for pinched/shorted wires very carefully.  If either motor lead is shorting to the frame, that is a big problem.

Yes.  Also make sure they are connected correctly.  Proper pair to brushes and other to field.  G

If you have a multi-meter check out everything on the loco. I have had one of my conversions turn up a shorted out lamp. This fried the driver board. Yes go back and check out every thing to be sure no shorts exist. Look at the leads to the motor and also the leads that pick up the power from the track. Double check everything against the wiring diagram ERR sent with the board.

Good luck

Ray 

Obviously, I'd check all the wiring, I just figured that the motor leads seemed a likely issue as you get the short when you start to move.

Did this run before adding the upgrade. Check your wiring, on the AC commander next to the heat sink you have a two pin connector and a three pin connector. The two pin is for AC hot and common the three pin goes to the motor. The wires comming from the three pin should be Yellow , Green and Blue. Yellow and blue are brush wires and the Green wire is the field wire. You can check for continuity if you have a meter. Look close at the caps, make sure the two leads are not touching.

Bill