W126 power window question
 

All four power windows failed today on my 1983 300SD. Fuses are O.K. Any quick fix ideas?

I never say anything is impossible, but this makes no sense. The windows have two separate circuits feeding them in a diagonal arrangement.

Does everything else work on the vehicle?

Is the engine running when you do the test?


Edited: Go directly to post #14 and perform the test.

i think there
 

may be additional fuses other than in the fuse panel. perhaps in the consol somewhere. i have not changed them myself but my indy has.

tom w

How old are the fuses?

My windows would stop working at random before I installed new fuses. It was odd.

Can you find out, please, Tom?

I don't know of any fuses for the windows other than the fuse box. Wouldn't make any sense to have two fuses in series.

Everything else appears to be fine. Engine is running during the test. All windows are up. Lock is not ON.

Maybe I'm totally off base here, but isn't there a relay behind the instrument cluster for the windows? Perhaps this failed?

Is it possible that there is a break in the elctrical supply BEFORE it gets to the fuse panel?
On some "other" cars, the accesory circuts in the ignition switch have different contacts than the engine "on" contacts--if that is the case, it is possible that wiggling the key switch may make the windows work.

This can be checked.

Hook up a voltmeter and check for 12V at both fuses that operate the power windows.

I don't have a W126 wiring diagram, but (for what it's worth) my W123 Haynes manual shows two window relays. I can't figure out what they do based on the diagram?

From what i remember... there is a connector right behind the panel to the right of your gas pedal check if that's connected fully.

On all my window work on the SD, power from the driver's center console gets sent directly to the windows, without any relays. I've been fighting a switch problem on the RR window for years (always putting it off) and mapped the various pin positions in all modes. It's a basic circuit that sends 12V and ground to the respective motor. On the rear windows, the power goes to the door switch first, and then onto the window motor.

The power is shown as going directly from the switches to the window motors, but there are also relays shown upstream of the "a" and "b" fuses. Maybe they are used to energize the window circuits when the ignition is turned on (to reduce the current on the ignition switch)?

That's certainly a possibility. If there is a relay used to reduce the power across the ignition switch, then the fuses will show no power.

This must therefore be the first thing to check.

See if there is 12V at the two fuses (a and b ??) with the engine running.

I agree, it looks like both fuses are fed from the same relay so that might explain all the windows failing at once. Remember, I'm not looking at a W126 wiring diagram so this should be verified for the correct car.