Hi,

A while back the power windows on my 1990 740 GL stopped working (not an instantaneous death, but rather a slow, sputtering one). I've finally gotten around to trying to fix the problem, but I'm a little stumped. I've been researching on the web and have tried a few troubleshooting steps that didn't fix the problem: first, I tried a new 30 ampere fuse (although given that the window controls died over time, it didn't seem like it was a matter of a blown-out fuse); second, I took out and dismantled the driver's side power window switch console (the unit with the switches for all four windows), using metal polish ("No harmful abrasives!") to clean the moving contacts (didn't seem very pitted at all) and stationary contacts in two of the four switches.

After cleaning, I reinstalled the switch, but still no luck (and I didn't hear any motor going); however, I just took out and dismantled the power switch again and noticed that little brown lines have reappeared on the moving contacts--does this suggest that power is running through the switch?

Do I need to do more work on the switch? (Do I need to clean up all four switches? And do I need to apply silver plating powder to the newly cleaned contacts?) Or does this seem to be a problem in the wiring? If so, how can I go about testing the various wires/circuits/relays? (I'm good at taking things apart, but I'm not much with electrical!).

Thanks very much for any guidance!