I agree that it could well be that switch. You have to remove the inner door panel to get to it. I have seen a number whose wires had disintegrating insulation, as did the engine harnesses of that era. Younger replacements can be found at the junkyard.

The lock cylinder part of the switch could also have come loose (if so, it can be reinstalled), but that would not explain all your symptoms.

Just to be sure, is the fuse intact, clean and firmly clamped in the fusebox?
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jds