I need to diagnose the failure of the driver's side back power window. Here is what it does: the master driver's switch does not work, and the switch for that window doesn't work. All other windows work. Because both switches do not work it leads me to believe that it is not a switch problem, but what could it be? The motor? Or, if the switch on the master switch fails, does that keep the one that goes with the window from working? Please let me know what you think.
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Darius in Albany NY '86 744 GLE, 91 745T

Narrow down the problem, pull the master switch, just remove the connector from the suspected bad window and put it in a known working switch. That will tell you if its the switch. The front switch and rear switch are independent. If it does work plugged into another switch, obviously the wiring is good. The window motor may be bad. Look in the FAQs, has a discussion.

well actually on your car, one switch can make both switches not work, like rod said connect to another good switch and try at the master, and then leaving that connected use the right rear switch to test at the left rear door, i think you have 1 bad switch.