The plug is under the step adjacent to the control box and motor.
Sounds more like a ground issue which is common. There should be two grounds. Locate them, disconnect them from the attachment to the frame or body. Clean connection good and re-attach. MAKE SURE YOU STAY CLEAR OF THE STEP!
As stated by previous post, disconnect linkage, make sure step moves freely. Good time to service! Clean pivot points with a strong cleaner, something like Brake Clean works. Then use a good quality grease. Chain lube works.