When my controller failed, it would't operate at all. When the controller detects the current to the motor increase it shuts off. It's possible your motor could be the culprit also. You can test the motor by touching the two leads to +12v and ground leads in the connector. (Be very carefull - the step will move and try to pinch you!) Reverse the leads and the motor will reverse. Good idea the check the ground lead also. As to P/N, I can't remember any more what mine was.
Have a nice day - Darrel
2007 3912 KSDP w/350HP ISL Cummins
2003 Grand Cherokee toad w/M&G Brake