Power window problems

the '88 928s4 that I bought in dec 1999 had some problems that I inherited from the Previous owner. One of them is the passenger power window being non-operational. First I thought it would be a fuse or so... but it turned out to be a bit more work.

1. both windows run on the same power and fused by one fuse only. The other worked, so, fuse is ok.

2. open the center console pass. side (2 screws) and check for broken wires. Use a voltmeter or test lamp to check the operation of the up/down toggle switch. You should be able to see the switch put 12v on the outgoing power cables to the motor. The switch actually connects in normal or reverse polarity causing the motor to go up or down. Very very non-sophisticated ;)

3. check for a loose connector just left of the relais panel in the center console. It can easily be pulled apart by accident.

4. open the connector of the cable that goes in to the door. It's a big connector just above the FI computer. On the bottom part of the connector you should be able to verify that power goes to the window motor when engaging the window switch. I used a voltmeter to do so, and after a few tests identified which pins carry the voltage to the motor.

5. now the fun part starts. Opening the door is easy. See the tips on Greg Nicols pages if required. Lift the window in the up-position and lock it with a piece of wood. Make SURE it can't drop when you take out the mechanism! Then undo all screws and takeout the mechanism with the attached motor. The motor has two culprits: one is that it is likely to get wet, and oxidation causes the motor to get stuck, and second: there is a fuse/overload device mounted inside (!@$@#$#@#!) the motor. Now: guess what caused the malfunction that I had with my power window...   Ok, when you open the motor (take the gearbox apart from the motor) do it carefully. The worm should rotate a little to release.  Take your time, and don't just full hard. You will damage the motor! When apart, you will see the connections going to the coils inside the motor, and two points that are actually the connections to the a.m. fuse/overload switch. I had to bypass them. The motor was ok. Using my voltmeter I verified that I now had a current thru the motor.

6. at this time it is a good idea to cleanout the gearbox, apply more grease, apply grease to the glider inside the door that is used to slide the window up and down. Check for excessive play of the slider. This is what causes the window to rattle when half open. So, check it out while you are down there.

7. next is the reassembling. As soon as the gearbox is in place again you can test the motor. Mark the up-position and make sure you match the markings as soon as you are ready with the outside test. Now the acrobatics start again, maneuvering the assembly in place. It's a pain, but that's the only way: thru the holes. You may need assistance and some small hands.

8. finally you enjoy the pleasure of a job well done when you push the switch again and watch the window slide up and down. There is one thing to bare in mind: the power should not be engaged too long. There is no max-current limit other than the fuse. Make sure you don't have a sticky switch. This may cause a burnout of the motor!

have fun,

Theo Jenniskens (the Netherlands)



today was the day that my driverside window got stuck at full-open. The alarm sounds as soon as I approach the car,
so repair was inevitable. It does not rain yet... but it will tomorrow ;-)

I opend the door, took off the covers, and had a look again at the windows mechanism. You just can't get it up again
without un-screwing the motor, so that is what I did. Took the motor with the gearbox off, and found out that it was
not running at all. 12V was on when engaging the switch. So far so good. Especially when you think for a moment that in my drivers door, all the wires that go to the window-motor have been worked on to locate broken wires. Seems PO's had trouble before ;-)

First I thought it would be the overload sensor inside the motor again, but this time it was ok. I took the motor apart, and saw the culprit. Water has entered the motor, and oxidized quite a bit. One of the brushes was stuck, causing
the motor to stop randomly, and work again if you hit the door (open/close/.....).

I took some pictures of what the motor looks like inside, and fixed it all again. Works like a charm. Fast, smooth,
and reliable. Cost: zippo!

If any of you need some help or photo's ... send me an email.
good luck to you all, and have fun!
'88 928s4 cherry red



On Fri, 14 Jan 2000, Johnny Billquist wrote:

> On Fri, 14 Jan 2000, Michael S Briggs wrote:
> > If no one else answers before I get home tonight I'll have a look in the manuals. A 91 "rest of the world" version...
> Please do. None else have given a useful answer yet. :-)
> > > As for what the problem is. I'd guess a power diode or something has a tendency to burn out. A problem with the design, I'd say. It seems to not  I'm curious if this is something that was changed after some point (to the
> > design in yours).... Only three wires coming out? Hm, for controlling both windows and the sunroof I would have expected six...
> Ummm. I said three connectors, not three wires. :-)
> Actually, it's something like 15 wires or so. But I guess the switches give (possibly) six, and then you have at least two per window.
> One feature is that you can close the windows with your lock. Just keep it at the lock position for about 3 secs, and it starts closing open windows and sunroof.

Okay, looking at the manuals now (your 91 is quite different from my 86!), the wires that go to the driver's side window from the regulator are green/red stripe and solid green (can't tell from looking which is for up or down). The green/red wire connects to pin34 (also labeled AR2 and 4, although there are several labeled 4). The green wire is connected to
pin 35 (also labeled 5. Oh! I assume that 34 and 35 refer to row 3, column 4 and 5 (or something like that).  "Row" 3 has wires 1-8). Oddly, pin 35 also connects to the passenger's side motor and the sunroof. But those wires are different colors. The manual also says that for Right Hand drive vehicles, AR1 and AR2 are reversed... Hm, AR1 is the connection to pin 33 for the passenger's side window. So for LHD vehicles, the passenger's side connects to 33 and 35, and the driver's side to 34 and 35. I'm assuming that the reverse thing means that for RHD vehicles, driver's side is 33 and 35, and passenger's is 34 and 35. Unfortunately I can't tell which one is for "up". Also, it's a little bit confusing why one of the wires from each window would connect to the same pin. Perhaps they aren't really connected together at pin 35, but instead pin 35 *can* connect them (such as when you hold the key in the locked position, and it wants to send a signal to close both windows and the sunroof. That would probably mean that pin 35 is the "close"  connection for each. Just a guess though. That's the green wireon the passenger side).
I hope that helps some. Since I haven't seen the unit itself, I'm a little confused by why the schematic shows certain things the way it does. Let me know if you need any more info.


For Johnny Billquist:
The wires coming from the left window motor are green and green/red (green/red means green mostly with a red tracer line on it). These wires go to a 12-pole connector (a connector with up to 12 wires running thru it - all poles of connectors are not always used) which is located "In driver's seat left." I do not know what that means. Maybe it is under or near the seat some place. Or maybe it means in the drivers vicinity.
The same color wires continue on to a four-pole connector in the console on the left side. At this connector, the green wire connects to a green wire, but the green/red wire connects to a black wire. These wires then go to the window switch. The window switch gets power from the window motor relay. This relay energizes when the ignition is on. When
de-energized, it sends power to the door lock system and shuts off the windows.

I would suggest removing the left side cover on the console and find the 4-pole connector. You can identify it by the colors of the wires going in and out. Just disconnect this connector and feed 12 volts into the green and green/red wires. If the window runs the wrong way, reverse the polarity of the connection. Since there are only two wires going to the window motor, it must be a permanent magnet motor rather than the usual brush motor which type will not reverse with reverse polarity.

You did not mention the model year of your car. This info is for a 928 from 78 thru about 82. If yours is later, let me know. I have the later wiring diagrams too.

Mike, I sent Johnny the wire colors. These window motors appear to be permanent magnet types and they only need two wires feeding to them. The polarity is just reversed for up/down.  He can't just short something at that connector. He has to unplug it and feed 12v in right there. It is so late you have probably already looked at your diagrams and slapped your forehead with a Homer Simpson 'Dho!"  But you were close.

For Johnny Billquist:
OK, so I went back and looked at the 91 schematic diagram. MUCH harder to read, some things are illegible. The diagram is much more complicated. Glad I have an 83.

Anyway, the wires coming out of the control unit under the seat are still the same colors: green and green/red. There is a connector, but is says that it is inside the door. Just disconnect those colors of wires from the control unit and connect 12 volts to them. Switch polarity if the window moves the wrong way.

If all else fails, get duct tape and clear plastic sheeting. Do you have duct tape in Sweden? Duct tape is one of the things that made America great. Can't get thru a day without rippin' off a piece.

At 03:48 AM 11/30/00, Finlay, Ian wrote:

>Hi all.
>With my drivers window stuck in the closed position (it's right hand drive) I took off the door panel last night to see what was going on. I can hear the motor try to turn when I press the window switch, and the lights dim very slightly if the engine isn't running. I therefore believe that the >switch is OK. It looks like there is a separate gearbox on the end of the motor - can anyone confirm this, and could it be stuck somehow?

A reversible electric motor drives a reduction gearbox, which moves a large gear segment with a lever arm attached. The lever arm has a nylon roller riveted to the end that runs in a horizontal track attached to the bottom of the glass.

The usual window problems are:
  - Bad window switch - the most common problem.
  - Fuse.
  - Relay.
  - Thermal breaker inside the window motor (often repairable).
  - Bad connection to the motor armature (repairable).
  - Broken wire.
  - Broken nylon roller at end of arm. (Replaceable separately - cheap
parts, not too easy.)
  - Loose bolts holding window lift unit to door. (POs and techs sometimes
don't torque enough.)
  - Worn motor bearings.
  - Dry lubricant in gearbox, worn gearbox.
  - Loose/worn nylon window guides.
  - Loose window guide tube.
  - Worn, damaged window guides at top.

I'm sure that the Listmembers can add to this.

>  I tried to get the two 10mm bolts out that hold the motor in, but they won't turn easily with a spanner. Is there a trick to it, or do I need more brute force?

I think that there are four, and they are very tight. They need to be. No trick. The two screws that hold the motor together and to the gearbox are also hard to remove.

BTW, it is possible to remove the window lift unit from the door intact.

Use extreme caution to hold the window in place. It can injure you if it falls on you, or can damage the car. You will need to manually raise and lower the glass while you are doing the repairs.

Wally Plumley
928 Specialists


On mine the rubber inserts on the gear stops (top and bottom) had deteriorated to the point that the windows would jam (wedge) in the full up or down position. BTW the whole assembly CAN be removed without taking the motor off. The stops (adjustable) are on each side of the assembly.

Dennis Wilson

Many thanks in advance . . .

Original Symptom: neither power window worked. I jumpered 30 to 87 in relay position VI and found that the passenger (US-- right) window switch and motor now work with the jumper but the driver (US-- left) is trying to work
(dimming dash board lights and making a clicking sound behind the door panel) but cannot. I am going to remove the panel and, I am told, will likely find a dirty power window motor that needs to be removed and rehab'd or replaced. Any suggestions or links greatly appreciated. Have not tore into it yet (many other errands on my "round tuit" list). Of course, my theory is that (1) I fried the 10a multi-purpose relay (928 intl says its the right one even though wiring diagram says 25 ampre fuse before hand in there) because the power window motor was drawing too much amperage trying to move. Not an electrician, so just a theory based on bits and pieces I've picked up re: this 928 problem. Again, thank you for any help, links you can send!

David A. Cmelik
81 5sp "moosgruenmetallic"



Your problem is probably the gearbox that is attached to the motor.
DONT keep the power on the motor trying to get it to run again.
There is an overload fuse inside the motor that will blow.
Could also be the bearings of the motor, when water has entered the motor. Then you're either taking it all apart, and cleaning, or you buy a used one. (I had it all apart... and it works fine ever since)

Taking the panels off from the door is fairly easy. There is a tip on Gregs site and i think on Dan's. A step-by-step if i recall correctly. Speaking from memory: two philips screws on the under side of the door, a few clips on the lower side, 2 10mm screws that hold the armrest, 2 more screws inside the map box just underneath the armrest, one philips screw underneath the door-lock-knob (pry off the disc on top of the knob, unscrew, and pull off), one screw in the door opener (philips type, small) and one screw where the air-hose enters the door.
Then you can take off the panel. Now you are gonne see the door metal plating, and see some plastic covering the holes in the plating.
These are the accesholes your hands will get stuck in from now on. You might want to shrink your hands now if you knew how ... are you any good in acrobatics? ;-)

You need to secure the window glass in the up position. Make damm sure it can not drop down as you work on the mechanism. The shield is really heavy. I used some wood and cloth to secure it inside the door.

You will see one cable entering the door and attaching to the motor.
It is only 2 wire. The motor is about 10cm*3cm*3cm, attached to a gearbox and the gearbox runs the "C" type of toothring that lifts the glass.
If you remove all 4 i think) screws the mechanism loosens, and you can manouver the motor so that you can take it loose from the mounting base.
When you have reached this point, it is up to you to carefully try to de-attach the motor from the bearbox. The gearbox can be openend if I remember correctly. Try to prevent pulling the rotor from the motor out.
You're gonna regret it when the brushes inside the motor have to be pushed back unto place by the rotor again. Ask me how I know... Oh yeah, the motor uses a worm-like gear on its rotor to run the gearbox gear.
So you cannot just pull it out, but have to "screw" it out.

I cleaned the gearbox, used some grease to make it run nicely again, and tested it thoroughly on a seperate 12v supply. Reversing the polarity simulates the typical up-down operation. When satisfied with the operation all mounts in reverse order. You will have to have a look at the lifting mechanism before you remove the wood that secured the glass position.
When finished testing the up-down of the glass, you may want to check on the window sliders. The sometimes have too much play, and cause a nasty sound while driving with windows partly open.

Hope this helps.


Hi I had a similar problem. My left window just stopped working one day without warning. Then it would suddenly start working again for a while.

I removed the door panel and checked the motor by applying 12 v to it and it worked. I then started to look towards relays, I have a 90 GT, which means that I have a control unit located under the left seat (rear footwell). That
was clicking when I activated the switch, put a multimeter on pin 34 and 35 and it was giving me 12 volts, so that narrowed down to a wiring problem.

It turned out that one of the wires to the motor was broken where it goes from the body to the door, more to the door side. Took my solder iron and fixed the problem, wrapped up with some electrical tape and window motor was working again.

90 GT


Is there any way to manually 'move' the driver's window UP temporarily? Mine decided to stay down.

alex v.
'86.5 928S auto ? meteor metallic (no spoiler!)


>Is there any way to manually 'move' the driver's window UP temporarily? Mine decided to stay down.

Most common problem is the switch. You can swap left and right switches (much faster than opening the door panel), or you can disassemble and clean the switch.

Wally Plumley
928 Specialists


always listen to Wally. It could very well be the switch as Wally said. You could also consider swapping left to right since there's a connector at the footwell about 50cm (30 inch) from the switch. If one window works, and the other one is stuck, its not the powerfuse obviously. Both windows are supplied by one fuse.

Manually moving the window up is a nasty one. Since the window is locked to the mechanism, and the mechanism is locked by the motor/gearbox there is no way that you can pull it up. You will have to open the doorpanel when you're sure power is supplied to the door.
Its not such a big deal though. 10 minutes if you've done this previously, and a bit more for the first time (http://www.nichols.nu/tip026.htm). First you can best take the cable connector from the motor and verify again that no power is supplied to the windowmotor. Next you will have to loosen the motor assembly from the door by unscrewing 10mm bolts (I think 4 of them). Then you can lift the glass and lock it by using some wood to support the glass and prevent it from rushing down on your hands again. This is critical!!
Then you have to take the motor loose from the window mechanism. That takes 2 more screws to unscrew. Now the fun starts, since you will have good access to the small electro-motor. I would take it to a workbench and use a volt-meter to check it out. Take it from there.

Some options:
bad contact on connector (oxidation)
broken internal fuse inside the motor
bad or broken motor brushes
motor internally broken or burnt wire

I have a bit of writeup on this subject on my web.
good luck, and lemme know if I can help.
'88 928s4 cherry red
The Netherlands



Add another possibility - the armature wires are simply crimped to the commutator segments. I had a motor that had lost electrical contact between the wires and the commutator. A bit of very careful scraping with the tip of a razor knife to remove the insulating coating on the wire next to the crimp, followed by a tiny bit of solder took care of the problem. No cost, except for an hour's work.

The "internal fuse" found in the plastic end bell of the motor is actually a thermal circuit breaker. It is not unusual for the contacts on the tiny little breaker to corrode, causing a lack of contact. Sometimes you can clean the contacts, sometimes you have to just bridge it.

Don't forget to clean and lube everything WYAIT, including the door latching mechanism.

Another interesting fix is to install several nylon wire ties around the nylon guide that surrounds the central tube. This will often greatly reduce the rattles heard when the window is partially down.

Wally Plumley