window switch question

[BerniniCaCO3]

This is for a friend's car and not an MGM at all.
But basically:
Window won't go up or down.
If neither switch works, the master switch OR the switch at the RR window, then it's not a switch problem (unless, for an odd reason, they both failed independently: or the RR window has its own dedicated fuse [it doesn't])?
So I will have to be looking at a motor, or a regulator?

that's all!

[tjc78]

Most likely, but I would still check with a multi meter just to be sure!

[sly]

what kind of car? some are actually all wired through the driver door panel... so it might be a wire issue.

[85crownHPP]

Probably a bad motor. Check for power/ground at the motor connector - it should be +/- one way and -/+ the other way (up or down).
If a regulator is bad, you usually hear delightful crunchy/grindy/stressed sounds when you try to operate it.
Smack the body of the motor with a small hammer and see if it springs back to life. If it does, replace it.

[BerniniCaCO3]

OK, hijacking my own thread.
Now this one IS for my 1990 MGM.

My driver's window gave me trouble. One day, just wouldn't go down, out of the blue. I expected that maybe my cheapie rebuilt motor installed 18mo ago may have already gone bad, so I pulled the door panel, got to the motor, verified voltage at the harness, and replaced the motor.
But the resistance value of the motor itself was fine. And the new motor worked where the old one didn't. So I concluded the bit of white built-up resistance on the harness was the whole story. This same rebuilt motor had also been wired in, by myself, using those splice connectors that cut through the insulation of two adjacent wires. I've since wizened up to the sketchiness of such connectors, so when the old motor didn't work and the new one did, I was satisfied that that must have been it.

Thought nothing of it, until a coworker borrowed my car and rolled down the driver window.
It wouldn't go up for him; dead, he said.

I tried it, it went right up, no hesitation. Then sent it down-- it stopped part way, tried again, went all the way.

It's like it's cutting in and out.
Where would you look to first?
Can high resistance in the wiring somewhere, result in a completely stalled motor? (and not just slower performance), or am I more likely looking for abrupt loss of contact, like intermittent contact in the switch?

With dying motors, I'm used to sluggish performance, like it's straining to go up or down. I'd expect the same from high resistance in the wiring, unless that's not necessarily the case; is it wiring or a switch do you think?
What I ought to do, is get a headlight, wire it to a window motor harness (I have an extra from the dorman motor), and then use THAT to check for power, cause it will actually be a load on the circuit. When you test circuits with a 10 megaohm multimeter, it can see 12.5volts in circuits that are barely holding it together, but the amperage draw of the multimeter is so small...

[sly]

I think the power windows are on a circuit breaker instead of a fuse. I'd check that first.

[gadget73]

next it does that, slam the door while holding the switch. If it goes, the problem is most likely inside the motor. The brushes are hanging up in the holder, or the commutator is dirty. The really crappy motors don't seem to hold up all that well, mostly because they are poorly sealed. I recently went through this with one of the original motors out of my car, a 1982 vintage part. The commutator was filthy. 5 minutes with some fine sandpaper to clean it up and the motor runs fine again.

[BerniniCaCO3]

Hmm, for a plan then, let me dig out the "old" (18mo) one and disassemble it and take a photo; you can tell me if it looks like a dirty commutator.
Could the new new window motor already be corroding in just a matter of 2 months?