My 2003 Envoy rear wiper does not work. It started to work once in a while, now not at all. I put another used one in it from a junk yard and it still does not wok. Could it be the rear body control module? The washer fluid still works. How can I test the pig tails that lead to the module to see if I'm getting power from the wiper switch. Also from the module to the wiper motor. That way I can try to narrow down the problem to the switch or the module.