1985 300sd Window PROBLEM. FR/LR fuse blows when ignition turned.

[W126Girl]

Hey guys,

All of a sudden the Front Right window and the Left Rear window would not roll back up today. I then looked at the fuse and replaced it. As soon as I turn the ignition the fuse immediately blows. I have blown about 7 fuses so far with zero progress! It just blows immediately.

The other windows work fine and that fuse is fine. What could be the problem and how can I get that window back up?

Thanks Guys!

[W126Girl]

I`m going to be so frozen if I can`t figure this out!

[tangofox007]

You could unplug one of the front console switches, then see if the fuse blows. If it doesn't, you should be able to get the opposite side window up. If the fuse does blow, reconnect the original switch, then disconnect the other side and try again. (I am betting against a short in both window circuits.)

[W126Girl]

Originally Posted by tangofox007

You could unplug one of the front console switches, then see if the fuse blows. If it doesn't, you should be able to get the opposite side window up. If the fuse does blow, reconnect the original switch, then disconnect the other side and try again. (I am betting against a short in both window circuits.)

Ahh, So in other words I hook the non-working windows (Front Passenger and Rear Driver) with the known working switch (Front Drivers and Rear Passenger) to get them up?

So we are looking at a short because the Front Drivers Side and the Rear Passenger work fine, its the Front Passenger and the Rear Driver that blow the fuse as soon as the key is turned.

[tangofox007]

Originally Posted by W126Girl

Ahh, So in other words I hook the non-working windows with the known working switch to get them up?

No. The objective is to eliminate one of the two offending window circuits at a time, in hopes of identifying which window is the culprit. (It is possible the the circuit is shorted upstream from the switches, but not probable.)

Originally Posted by W126Girl

So we are looking at a short because the Front Drivers Side and the Rear Passenger work fine, its the Front Passenger and the Rear Driver that blow the fuse as soon as the key is turned.

Diagonally opposite windows share a common fuse, as you probably have figured out. Downstream from the fuse, each window is wired independently. From a given fuse, one wire goes to the left switch and one to the right switch.

If the problem turns out to be the rear window, it is easy to jumper the door switch to get the window up.

[Jeremy5848]

You may have a short in the cable that runs from the B-pillar into the left rear door. In the 1980s W124 cars, this is a common problem. The wire used in that era was not sufficiently flexible and gradually break over time. Your S-class may have a similar problem.

To find the broken wires, you must remove the left rear door skin and the left B-pillar cover, disconnect the window wires at the left rear switch, and pull them back into the B-pillar. That is how I found and fixed a similar problem in my '87 300D Turbo. See here for details of that job.

Jeremy


Jeremy

[W126Girl]

Originally Posted by tangofox007

No. The objective is to eliminate one of the two offending window circuits at a time, in hopes of identifying which window is the culprit. (It is possible the the circuit is shorted upstream from the switches, but not probable.)

Ahh okey~

I`m kinda learning as we go. So lets say these are my window Switches:


1 2

3 4


Ok, 1 is the front driver and 2 is the front passenger, 3 is the rear driver and 4 is the rear passenger switch.

Which do I disconnect first and which second if the first one doesn`t nail down the circuit?

[tangofox007]

Try 3 first. If the fuse doesn't blow, raise the front window.

[W126Girl]

Originally Posted by Jeremy5848

You may have a short in the cable that runs from the B-pillar into the left rear door. In the 1980s W124 cars, this is a common problem. The wire used in that era was not sufficiently flexible and gradually break over time. Your S-class may have a similar problem.

To find the broken wires, you must remove the left rear door skin and the left B-pillar cover, disconnect the window wires at the left rear switch, and pull them back into the B-pillar. That is how I found and fixed a similar problem in my '87 300D Turbo. See here for details of that job.

Jeremy


Jeremy

Thanks for the info! My fuses blow as soon as I turn the key without even pressing any window buttons. Did you have the same experience?

[Jeremy5848]

Unplug both 2 and 3 – those are the windows that blow fuses, right? KEEP TRACK OF WHICH SWITCH GOES WHERE. Then replace the fuse. If you can start the car without blowing the fuse, you know that the short is after the switches.

Next, replace 2 and try to roll up the front window. If it goes up w/o blowing the fuse, you know the problem is in the rear window. If the fuse blows, try putting switch 3 in place of 2 – it might be a bad switch. If the fuse still blows, you have a problem in the right front door wiring.

If the right front is OK, then the problem has to be in the left rear. Next, remove the switch from the left rear door (as well as the console switch 3, which is already out). With both switches out, the fuse shouldn't blow. Now put console switch 3 back. If the fuse blows, the short is in the wires between the console and the door. If not, the problem is in the door.

Note that both rear door switches (console and door skin) must be in place for the rear window to work.

[Jeremy5848]

Originally Posted by W126Girl

Thanks for the info! My fuses blow as soon as I turn the key without even pressing any window buttons. Did you have the same experience?

No, I had to press the switch to blow the fuse. Hmmm, that may mean that your problem is ahead of the switches.

[W126Girl]

Originally Posted by tangofox007

Try 3 first. If the fuse doesn't blow, raise the front window.

Thanks!

Now on to find out how to Disconnect these window switches. I think I saw something in the DIY section. Starts with taking the ashtray out etc.. I think.


So that should allow me to get at least one of the windows up if I understand it. Then the other can be made to go up with a jumper wire. Can I make a jumper wire out of a Cigarette Lighter Plug in that was used for a CD player?

The jumper wire connects to the battery and (insert location, because dumb dumb W126Girl doesnt know where)

[Oracle12345]

sounds like a short circuit or short to ground.

[W126Girl]

Originally Posted by Jeremy5848

No, I had to press the switch to blow the fuse. Hmmm, that may mean that your problem is ahead of the switches.

Is that a good thing or a bad thing? eek!

[tangofox007]

Originally Posted by Jeremy5848

Hmmm, that may mean that your problem is ahead of the switches.

Power is supplied to both sides of the motor when the switches are in the neutral position. Actuating the switch opens one positive circuit and closes that circuit to ground.