Mercedes Power Windows've got power windows that don't work, or work intermittently.  This procedure will also work in the dreaded "the #@%$ng window just disappeared in the door and it's freakin' cold/raining!" emergency.


First you gotta' understand how they work.  All that confusing mass of wiring, swiches, etc. does is reverse the polarity of the power going to the little electric motor in the door.  The motor has two wires coming out of put 12V+ to one, and 12V- to the'll go one direction.  Reverse this feed and it goes the other way.

The pictured guinea pig is a W201.  This basic procedure works an ANY Benz I've ever tampered with.

If the offending window is a front, pop up the console plate, unplug the wires offa' both switches (and remember where it all goes)....if it's a rear, pull the rear door switch out of the panel (there's enough extra wire to pull the rear switches out a couple inches, which is all you need).

Don't try to test a "rear" window motor from the "front" switch.  Trust me on this.  Check the "fronts" from the front, and the "rears" at the door switch.  

Mercedes-Benz is kind enuf' to number those little black connectors.

Number 1 and Number 2 (the two in the center of the connector) are the two wires going to the motor. Always.  Always.  With the switch removed from the plug(s) the window motor is effectively and completely isolated from the entire vehicle wiring harness.

You need an external 12V power source.  I use my handy-dandy "jumper box", and two incredibly low-tech chunks of #10 wire. pwboosterpk.jpg (79258 bytes) (use HEAVY wire.  These motors consume a fair amount of current...).

Locate #1 and #2 in the offending switch connector (door panels don't have to be off....our test subject in these pics was being stripped of the interior and in the warm shop, so it's the one I picked).

At the rear door switch checking a "rear" pwrearconn.jpg (47098 bytes)

Under the console plate checking out a "front".  left front connector pwlfrt.jpg (91600 bytes) ....and the right front connector. pwrtfrt.jpg (88299 bytes)

Put yer' jumper wires in #1 and #2. pwrear1.jpg (58306 bytes) pwrear2.jpg (66689 bytes)   Just sparks and groans...or just sparks?  Switch 'em.  (Nice job on the thumb with a hammer, huh...)

  1. The window didn't go somewhere (up or down) the motor's history.  If it's a W201 or W123....I've got one.

  2. If it DID, in fact, go up or've got a wiring or a switch problem, and you need some electrical knowledge, an understanding of the system {ie: a wiring diagram , and a VOM and some long test leads}.

Other tips.

Rear window works from front, but not rear.  The "kiddie lock" button on the front driver's side can be eliminated as a cause by simply removing the two-prong plug and jumpering the two (both brown wires) terminals. pwkidlock.jpg (94542 bytes)

Front switches are all gunked up with spilled coffee/pop/beer etc.  Take the front switches, soak 'em in HOT water for a half-hour or so, and then dry 'em with compressed air.  An alternative is take 'em outta' the car and rinse the daylights out of them with "contact cleaner" but the solvents in (good) contact cleaner screw up the cosmetics.

Rear window won't work from front OR rear....but works when "jumpered" at the switch.  REALLY common on W201 sedans....  This is where the aforementioned "electrical knowledge, an understanding of the system {ie: a wiring diagram}, and a VOM and some long test leads" comes in.  You've probably got a broken wire...and it's apt to be where the wiring "flexes" going between the "door" and the "pillar".  Remove the pillar trim, check continuity (while doing this, you need to have the "kiddie switch" connector jumpered), and fix it, or splice and run another.  I do it all the time on customer cars.

Window operates ok except for one hell of a clunking/grinding/banging noise when it gets to the top.  REALLY common on W123 cars, especially rears.  It's probably because you ignored the fact that the bolts holding the riser to the door were loose.  I've even seen them crack the inner door shell.  The torque of the motor twisted the beejezus outta' the cast bracket part of the riser assembly....and it cracked.  (I've got used ones that aren't....)



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