So after hours of reading on here, I think I understand the system. When the trans is shifted into reverse, the switch powers the relay to send power to the rear diff. On the rear diff there is a "solinoid" that is vacuum opperated that engages to allow the diff to operate when in reverse. Once shifted out of reverse the soliniod releases. If I unplug the relay, the switch on the trans, or the rear diff wiring, the system should not work, and if it is my problem, it should not appear. The relay part # is 191 957 917. I should be able to find this under the dash.
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