I disconnected the wires at the junction box beside the step. Then using jumper wires, touched the positive to one motor wire and ground to the other, then reversed the wires. If the motor works, it's the controller, if not, the motor is bad. I don't recall now if I had to cut the wires from the motor to the controll box or is they had a disconnect. The controller is just a reversing switch that tells the motor which way to turn and when to stop. As I recall, the magnetic switch makes a connection (i think it is normally open) and tells the controller to activate the step. On mine, I could actually hear the controller "click" when the door was opened and closed, so I knew the magnetic switch was okay. I aasume you have already tested to see if you have 12 volts at the connection going into the box?