1989 Sedan Power Window Problem

[Fixedit]

I've spent the day trying to diagnose a power window problem on a sedan, been searching the forums, studying wiring diagrams, and tested everything to my abilities and I'm still stuck with the issue.

The driver front, driver rear, and passenger front windows all work. They work with the driver door switches, as well as their own switches on each door.

The passenger rear works intermittently. It works great when it does, fast and smooth (ruling out dirty regulator tracks). I have tested the driver switch as well as the passenger rear switch, both are good with continuity and both are sending power correctly.

The window motor itself is tested to be good, I removed it and jumped it to test both directions just fine. Re-installed it to continue testing.

Power is reaching the motor, I have tested good power at its harness plug for both directions. Yet it does not operate. Fuses are good.

Since both switches are good, and power reaches the window motor, and the motor is good, I don't see how it fails to operate. The motor is case grounded so I checked the engine harness ground connections, which were fine (no surprise as all the other windows work no problem).

Has anyone had a similar problem, and if so, is there a common place for corrosion in the power window wiring or something (what was the fix)? That's the last thing I can think of, is somewhere I've got a corroded ground, but I keep ruling it out since, when it does work, the window is fast.

Thanks for reading and once I have this figured out I hope it can help someone else in the future. I've searched this site for this problem but only came up with more common issues that I've been able to test for.

Quick edit: I've plugged in another known-to-be-good motor and grounded it to the door, but it also does not turn.

[Dr_Snooz]

If the brushes in the motor are worn out, it will act exactly as you describe. A good whack on the case of the motor will start it working again when it stops. It's not often that brushes wear out in a rear window, admittedly. Usually it's the driver window that's getting used all the time. Nevertheless, you can rule it out pretty easily with a good whack.

[Fixedit]

Yeah I thought about that, thinking of starter motors, but I tried hitting it quite a bit with no effect ):

What I truly don't understand is why another known-good motor doesn't work if I plug it in and ground it to the door/regulator assembly. Makes sense to me that that's enough to simulate being installed, but for peace of mind tomorrow I'll try fully installing the good motor to check. After that I'm gonna either move the original motor to another door if possible, OR move a good motor from a different door into the problem door, either way I'm hoping that will help me determine which is bad: the motor or the circuitry. That is, if installing my good motor doesn't work.

If none of that musical-motors dance gives me anything, it's on to checking all of my wiring. Might even swap in known-good switches if I feel like taking apart my daily

[Oldblueaccord]

run an xtra ground wire just to make sure the motor is grounded good. You got good voltage it should run.

Permanent magnet motors get weak over time and need replacing.

[Dr_Snooz]

The trick is to whack the motor while you have the switch activated.

What happens to the power if you flex the loom where it passes from the door pillar to the door?

[Fixedit]

Funny you should ask that because I found the problem in the door pillar. There's a connection in the pillar frame right before the harness makes its way to the door, and for some reason one wire (Green, from driver switch to door switch on the "down" side of the circuit) was just barely corroded enough to have a bit of resistance capable of stealing the power from the motor. Cleaned up the connector a bit and now everything works great. So glad to finally have found it! I feel silly for having tested everything else before checking there but I don't care haha I'm just glad it all works. Thanks for the help and ideas. I was second guessing all of my knowledge and didn't know what to do but ask for help; now I know I'm not crazy and I was actually doing it right haha

[Oldblueaccord]

Funny you should ask that because I found the problem in the door pillar. There's a connection in the pillar frame right before the harness makes its way to the door, and for some reason one wire (Green, from driver switch to door switch on the "down" side of the circuit) was just barely corroded enough to have a bit of resistance capable of stealing the power from the motor. Cleaned up the connector a bit and now everything works great. So glad to finally have found it! I feel silly for having tested everything else before checking there but I don't care haha I'm just glad it all works. Thanks for the help and ideas. I was second guessing all of my knowledge and didn't know what to do but ask for help; now I know I'm not crazy and I was actually doing it right haha

Voltage check with a meter unloaded and loaded probably would have caught that.

[Fixedit]

It was only dropping around 0.04V and I didn't think that was enough to prevent the motor from working, but I was definitely wrong about that

[DBMaster]

I actually had the power window control module go bad in my 89 LXi coupe. It was the last thing I replaced before I gave up the car due to an accident. My driver's side window would fail to work intermittently. I found a NOS module on eBay for $95 at the time (2012). That was the fix for me. It's basically a small black box mounted in the door behind the trim panel.

[Oldblueaccord]

It was only dropping around 0.04V and I didn't think that was enough to prevent the motor from working, but I was definitely wrong about that

if its a DMM sometimes that autoscaling feature will not flip quick enough and that .04V was 4v. If your pretty sure, like in this case, you are work on a 12VDC system manually setting the scale helps.

[Fixedit]

Ah okay, that does make sense (especially since my meter is by no means modern). Thanks!