Volvo: 1990 740 power window failure, power window switch, instantaneous death

Question
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 might this be a dead window
motor? Or does this seem to be a problem in the wiring? If so,
how can I go about testing the wires?

Thanks very much for any guidance!

Answer
Larry,
First test for power to any of the wires in say the LF switch. If you do have power then perhaps cleaning or renewing the switch will fix the problem. No power trace back to the relay or the fuse. Often there are more then just one fuse that controls the windows. Look carefully at the wire connector to the switch and you will see two wires that go off in a different direction a red and black wire. Those are to the window motor itself. With test leads ground one of the wires and put power to the other, does the window move? Change position of the test wires will the window go in the opposite direction? If you are getting movement then all the problems are in the power, grounds or switches. You may want to purchase new switches.