Here is a diagram for most Kwikee steps. They have over the years switched the magnetic switch from normally open to normally closed, wait was it normally closed to normally open.
Kwikee step diagramYes the switch does provide a ground to the controller but it is not a good ground for testing. If you had a multimeter it would be used to verify switch operation. If your test light has a continuity operation, it could be used for checking switch.
Best ground for testing would be one to frame. You could take the motor ground, large green wire, loose from the frame, clean the frame good, reattach and use it for testing and ground for motor.