Check the speaker wires in the door -- the seat switches are hot when the door is open, and if the insulation is worn between the seat wires and the speaker wires, the speaker will be, too.

My brother and I spend forever trying to get the power windows to work reliably in his old Buick -- passenger sides would go down but not up, replaced switches, checked motors (all good), finally looked at wires -- all of them were crimped and most were broken. A couple hours of soldering in VERY tight quarters, and all the windows work again.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!