What sound decoder have you had secses with installing and running on a athearn RTR gp40-2. The one I'm talking about DOES NOT have the quick plug.
Make sure the motor is isolated from the frame. Because it's rtr doesn't mean a thing. If you don't see 2 wires going from each truck to the lightboard and motor it means the motor is most likely grounded to the frame.
Dr. Frankendiesel aka Scott Running BearSpace Mouse for president!15 year veteran fire fighterCollector of Apple //e'sRunning Bear EnterprisesHistory Channel Club life member.beatus homo qui invenit sapientiam