my back windshield wiper turns on once i turn OFF the car.

sounds like a grounding issue to me. you may have a loose grd wire or it may be dirty and not making good connection

Possible failed 'alarm and relay control module'.right side behind glove box. TEST input and output signals.Service manual best , for reference.-------P.S. , I know it says "alarm and relay" control module -nothing about wipers , but it does contain the wiper controls.