we installed 3 traction cars a couple of years ago. the mechanic left the car on cartop for the night while doing the mod, the next day he came and the car had moved from where he left it, a couple of floors. he thought it was strange but all seemed ok, so he moved on. a while later, same thing. he was on the car when it moved by itself. very dangerous. so he continued the mod and always pulled stop switch. smartrise told him to recheck all wiring, but he found nothing wrong. any way he finished car and moved to next car. sure enough he was getting the same thing. now we knew it was not a fluke. I believe the it was induced voltages from the trail cable. you could see some of the input led on lightly. any way smartrise came out and installed relays in the inspection circuit. and it solved the problem. the cars have ran great for the last 2 years, rarely a call.