Rear driver power window doesn't work - not a fuse problem - PeachParts Mercedes-Benz Forum

MercFan · #1 12-03-2012, 05:30 PM

I've checked the fuse with an ohm meter - it's good. All the other windows work just fine - it's just this one is busted. There isn't any noise and it doesn't matter if I use the switch on the shifter console (between seats up front) or the switch directly on the door - same thing.

I guess taking apart the door panel would be next to make sure I get voltage to the motor? Are these window motors prone to just giving up!?

davidlee · #2 12-03-2012, 06:58 PM

Hey hows it going, I have the same problem in my 87 300D, but my window motor works just fine if I hard wire it to power and ground, I have a broken wire or a bad ground somewhere in between the front switch and the rear door switch.
Im not sure if this will work or not but, you can wait until the evening time and turn on your lights and see if the window switch lights up, if not you might have a bad ground somewhere or broken wire somewhere, if it lights up, then remove the door panel, ( its very easy on the 126's ) and trace the wires leading to the motor and test for power, if there is power then you might have a bad motor, you also might just have a froze up motor, I have got countless power window motors to start working again by hooking up the motor wires to a 18v drill battery and alot of times it will free them up and then you can hook the wires back up to the car, and it should work fine.

MercFan · #3 12-03-2012, 07:30 PM

Thanks David - I just checked (it's dark now...

and all of the window switches light up at the console. The switches on the rear driver door are all illuminated: one of them moves the back seat back and forth and the other is for the window. So it sounds like I've got power to it. Sounds like I need to take the door panel off next. Thx very much -

MercFan · #4 12-03-2012, 08:22 PM

If the motor was seized up - wouldn't I hear it struggling a bit, or at least humming?

davidlee · #5 12-03-2012, 10:15 PM

If you have the door panel off you might possibly hear a small sound omit from it, but some times not, I have been able to unstick motors using 18v that I thought for sure where done for. If you have an 18v batt, It doesn't hurt to try. if it works you will get a smile on your face, and if it doesn't, then you already have the panel off for replacement.

tram · #6 12-04-2012, 04:35 AM

Pop the rear switch out and unplug it. You should have power at both the green and black wire going TO the switch. These are striped wires. The plain green and black go to the motor.

I just went thru a similar problem on a 1985 300TDT. The wires in the rubber boot between the pillar and the rear door broke in the boot... causing my FAVORITE type of problem... INTERMITTENT. I ran new ones from the pillar through the boot and into the door, then soldered them to the old wire and heat shrink- ed them. To access the wires in the B pillars, just unscrew the plastic base and pop off the cover.

If one wire is broken, replace all three in the boot. For some reason the blue illumination wire never seems to break- maybe because it's smaller.

If you want to cheat, cut the sheath the wire runs in, and splice your new wires to your old ones- solder them. Make sure you don't have any burrs in your solder joint and pull them through.

On the RH side, if I recall, the wires in question are blue and black with stripes.

Replace your brown grounds too- the same way.

Oh, and there's an easy way to tell if it's a locked motor- it'll draw enough amps that you'll be able to see your instrument warning lights or your courtesy light dim slightly when you hit the switch.

rscurtis · #7 12-04-2012, 04:14 PM

Turn on the dome light and operate the subject window without starting the engine. If the light dims slightly, you have a motor (probably bearing) problem. If the light doesn't dim, you have an open circuit somewhere in the system.

charmalu · #8 12-04-2012, 11:14 PM

Post#6 in the following thread shows a motor taken apart. You might be able to get it to work with some lube etc....

Anyone replace a window motor in a w126?

I have a 14V Drill motor I use to check window motors, Blower Motors and move electric seats.

Charlie

Diesel911 · #9 12-05-2012, 12:02 AM

If yo need to remove the Door Panel inside where the inside Door Pull/Opening lever is; is a Plastic cover under the Lever opening that needs to be pried out; under that is a single Screw that needs to be removed.

If it turns out that the Motor is working but the Window is not moving the Window Regulators are prone to bending after which the Gear Teeth on the Regulator wear out.

vstech · #10 12-05-2012, 04:53 AM

of the thousands of door motors I've pulled, the most common is dried out grease in the gearbox. next is rust in there from water seeping past the sills... then it's the loos bolts from the regulators tilt the angle enough to grind off the teeth from there and the window no longer will raise/lower.