Which wire makes the window go down?

[rammstein]

Car is a 91 318 sedan. Driver's side rear window will only go up, not down. I got it to go down a few times as I messed with the switch, but the problem exists regardless of which switch I use (front or rear), so I am led to believe that perhaps a wire has become compromised. I also think this could be true because a previous owner had changed the front switches to E36 switches which required some wire splicing. I'm 100% sure the motor is fine, as if I connect it to the right side for testing it goes up and down without any problem whatsoever.

Anyhow, does anyone know how to tell which wire corresponds to UP and which one to DOWN?

Man, I am SO close to having this debacle finished. I finally replaced the driver side rear door lock actuator and it WORKS!!! Once these windows are working, the car should be nearly 100% again! Sadly, I may then decide to sell it as I just don't have the time to keep up with it anymore, but I wanna be sure its in good shape no matter what.

Thanks fellas!

[Gregs///M]

Two wires are required, not one. Switching polarity will switch the window up or down.

Download the ETM and it will help you big time.

[rammstein]

Two wires are required, not one. Switching polarity will switch the window up or down.

Download the ETM and it will help you big time.

Not sure what ETM is, but if its the same as the electical diagrams in the bentley then I have it.

There are 2 wires coming that go from the front window switch to the back. That much I know, I just assumed that the way it works is you complete the circuit one way by pushing up which I assume sends 12 V to the window motor through one wire, or pushing down and it sends 12V to the window motor through the other wire.

Here's a question- if the switch in the front was somehow bad, wouldn't the rear switch still work? That's why I am assuming this is a wiring thing.

[Gregs///M]

If one of the switches failed, the rest will continue to work.

The ETM is the electronic troubleshooting manual, its separate from the Bentley and much better. search e30 etm.

[rammstein]

Cool- I actually have that manual, so I guess I'm in good shape on that front. Looks like its time to bust out the multimeter. I'll post back with results.

[rammstein]

OK- Now this is REALLY perplexing.

I took the multimeter and began by measuring voltage at the 2 wires going to the motor. When I push the switch one way, I get +12.4V, and when I push the switch the other way, I get -12.4V. So how the hell does the motor only go one way? Just to make sure I ma not going crazy, I hooked the motor up to the other side, and it goes up and down no problem. The motor is fine, and now I come to find out that the motor is seeing + and - 12V as it should, so how in the hell does it only go one way on my driver's side? I don't get it. I hate this. If it has shown like 0v on the down side, then I'd know there was something wonky going on, but now what? UGH. Seriously, this is the worst.

[StereoInstaller1]

OK- Now this is REALLY perplexing.

I took the multimeter and began by measuring voltage at the 2 wires going to the motor. When I push the switch one way, I get +12.4V, and when I push the switch the other way, I get -12.4V. So how the hell does the motor only go one way? Just to make sure I ma not going crazy, I hooked the motor up to the other side, and it goes up and down no problem. The motor is fine, and now I come to find out that the motor is seeing + and - 12V as it should, so how in the hell does it only go one way on my driver's side? I don't get it. I hate this. If it has shown like 0v on the down side, then I'd know there was something wonky going on, but now what? UGH. Seriously, this is the worst.

What you are dealing with is called "rest on ground"

How it works is simple but confusing. Both wires, when the circuit is "at rest" show a ground. When you push the "up" button, the "up" wire goes to +12V and the "down" wire stays on ground. Obviously, when the "down" button is pressed, the down wire goes live and the up wire rests on ground.

Now, here is the confusing part: if you press the up button and the ground is disconnected, the down wire will go live too, because it feeds back (complete the circuit) through the window motor.

Pull the switches, refer to the ETM for color codes and test continuity to ground at the switches first. I bet its a broken ground under the center console...hope its that easy!

Luke

[rammstein]

What you are dealing with is called "rest on ground"

How it works is simple but confusing. Both wires, when the circuit is "at rest" show a ground. When you push the "up" button, the "up" wire goes to +12V and the "down" wire stays on ground. Obviously, when the "down" button is pressed, the down wire goes live and the up wire rests on ground.

Now, here is the confusing part: if you press the up button and the ground is disconnected, the down wire will go live too, because it feeds back (complete the circuit) through the window motor.

Pull the switches, refer to the ETM for color codes and test continuity to ground at the switches first. I bet its a broken ground under the center console...hope its that easy!

Luke

OK- Here is where I play my moron card- what do you mean when you say test continuity to ground at the switches? I have the ETM so that's a start. What makes me suspicious is previous owner did a swap to e36 switches in front, and I already years ago had an issue where I ended up redoing a lot of the soldering up there.

[rammstein]

Interestingly, if I hook up the multimeter to the two wires going to the motor and measure AMPS, now its doing what I would expect- it shows a reading for UP but 0 for down. I have no idea about the science of what is happening here, but at least now I have confirmation that for whatever reason the down button isn't juicing the motor with AMPS.

[rammstein]

OK I used google and what checking continuity to ground means is hooking black to the chassis and red to the various spots on the window switch and making sure I get a beep. I'll report back.

[StereoInstaller1]

Yep, exactly. Make sure the brown wires are solid ground..the hackery is another story.

Post some pics of the carnage if you must...LOL

Best of luck, and I hope the explanation helped.

[rammstein]

Well THAT was fascinating. So I started trying to disassemble the front window switch to get at the ends of the wires for testing. I popped off the switch rocker and two metal clips went flying. After spending 45 minutes trying to find them, then using a magnet to get one of them out from the under my seat, I started trying to put it back together. Something strange happened then- I pushed on the window button and the sucker worked. WTF?!?! worked in both directions. Tried it from the back, it worked there too. So then I clicked the switch all back together, and BOOM, no more window down. I pried it apart, and I can get it to work again. SO this means, I'm gonna go ahead and guess, that the window front window switch is somehow bad. This perplexes me a bit as I thought that even if that switch was bad, the rear would still work, but apparently I am mistaken. I think this means I need to get a replacement switch for the front.

Here is the offending switch:


What's weird is there is this slider component to it that appears like you would slide it to eject the top, but it only slides like a mm or two and barely starts to pop apart, then that's it. No amount of force seems to work as far as getting it apart more.

So I need to find a white-backed e36 window switch, right?

[rammstein]

IT WORKS!!! So I looked up white-back e36 switches on EBAY and it turned out there were a pair listed from a guy in Ft. Lauderdale. I took a shot in the dark and wrote him, told him I was a forum member in case he was too, and as it turns out he is and I drove the 35 miles to his house, got the switches, came home, and everything works now. My window goes up, and down, and up again. It is incredible. Awwwwwwright!!!! Now I just have to put everything back together and fix a few more nagging things and the car should be 100%. Awesome!