Good idea on diagnostics from Charles.

I found on mine that the switch would work, sometimes, with the door open but not closed. This indicated a wiring/short problem. The wires become quite brittle over time with all the opening and closing right at the bend for entering the door.

I ended up pulling the trim piece on the b pillar to access the wires on that side of the door. I spliced in some new wire with solder & heat shrink and all is well. Once I cut the wire and pulled it out it was obvious where the problem was.

If Charles' idea works to diagnose the problem (rules out switch and motor) then I would suspect wiring at the door as the problem.

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83 300d - 390k