When I bought my 84SD neither of the two rear windows worked. I took out the switches and cleaned the internals and both have worked flawlessly for three years. A year ago my front passenger window stopped working. I cleaned the switch. Still nothing. So then checked for voltage at the motor next. It was getting voltage so it had to be the motor. Before I bought a new one I figured I would tear it apart. I did and relubed everything and put it back together and bench tested it. It worked. So I reinstalled it and it has worked ever since.

Next thing you need to do is check for voltage at the window motor while depressing the switch both directions.

IMO, most of the time it is not the actual motor itself dying. It is the switch, wiring, or stuck gears.

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2009 ML320 Bluetec
1985 300CD
1981 300TD

Past Mercedes
1979 300TD
1982 300TD
2000 E320 4Matic Wagon
1998 E430
1984 300SD
1980 300SD