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Old 04-07-2012, 04:57 AM
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Join Date: Jan 2012
Location: charlotte n.c.
Posts: 40
Question rear windows 87 300td

Both rear windows will not open check fuse and ok..cannot believe both motors died. Some mech beat on my door with his fist for awhile and got one to work for five minutes....Strange repair procedure.
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Old 04-07-2012, 02:07 PM
Jeremy5848's Avatar
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Join Date: Mar 2006
Location: Sonoma Wine Country
Posts: 8,393
Look in the B pillars

Originally Posted by callocco View Post
Both rear windows will not open check fuse and ok..cannot believe both motors died. Some mech beat on my door with his fist for awhile and got one to work for five minutes....Strange repair procedure.
The most likely problem for your problem is the child-lock switch in the console. If it has been accidentally left in the "off" position or if the switch or its wiring have failed, the rear windows will work from the console but not from the rear door switches. By my reading of the schematic, even a missing child-lock switch should still allow the rear windows to be operated from the console. If that is not the case, read on.

The '87 300D/TD and some other cars of the 124 era have stranded wiring in which the individual strands are too coarse. Over many years of bending back and forth in the rubber accordion that runs between the doors and the A and B pillars of the frame, the copper work-hardens and the strands begin to break. Eventually, there are so few that they cannot carry sufficient current and the windows stop working (this can also affect the puddle lamps in the bottom of the doors). In the case of my '87, the broken wires eventually protruded through the insulation and caused a short circuit so that I was continually blowing fuses.

Although a coincidence, it is entirely possible that the wiring to both doors has failed at about the same time. To test this theory as a possible cause, remove the door skin(s) and disconnect the wiring at the bottom of the door where there is a two-terminal screw connector. Those two wires go to the window motor. You can apply 12 Volts across those two wires and see if the motor will go up or down. Reverse the leads to make the motor go in the opposite direction. If that is successful then you know the motor is good. If it fails, the motor is almost certainly bad (assuming you have the right wires).

If the motors are good but still don't work from the console or door switches, then it is either a switch or a wiring problem. The switches I assume you know how to work on and there are many threads in this forum on repairing them. Wiring in the console is usually not a problem because there is no movement of the wires so they don't break.

To check the wiring in the B pillars, you need to remove the covering. The plastic cover at the bottom is held on by two Phillips-head screws and the pillar cover has a sheet-metal fastener at the top that clips into the B pillar itself. You will have to unreel some of the seat-belt to get the cover away from the B pillar so you can look inside. It may also be necessary to disconnect the wiring in the door so you can pull it partially through the rubber accordion -- if the wiring is broken it will probably be in the accordion, where all the bending takes place. Any broken wires that you find can be repaired or replaced and the door and B pillar put back together.

Note that my advice is for an unmodified car. If someone has been boogering with your car's wiring, all bets are off.


"Buster" in the '95

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Old 04-07-2012, 09:27 PM
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Join Date: Mar 2006
Location: Mount Holly, NC
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in addition to the wiring... on the 124, the rear windows are on tracks, and thin wires connected to a plastic clip are on the lift... they break, and bind the motor. have fun...
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Old 04-08-2012, 05:41 PM
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Join Date: Mar 2012
Location: Portland OR
Posts: 548
Lots of good advise. I found that 75% of the time that the window motors dont go out, They tend to freeze up after a while of not ever getting used. I took my door panels off the rear, disconnected the motor electrical connection and sent 18V to it Via a cordless drill battery. If they are froze up, that should free them up. and as long as you are driving the car on a daily basis and using the rear windows once in a while they should work fine.
The reason I tend to think this might be your problem is because you said the Mech. banged on your door till one started working. I had the same problem on my 190E.
I took 18V to both of them now they work 95% of the time, the other 5% I have to hit the door panel While using the switch.

Old Merc's Like everything to be used all the time,
When they sit, things tend to stop working for a bit.

David. Portland Or. USA
87 300D #22 head [1 year of ownership ]
87 190E 2.3 [6 & 1/2 years ownership} No Major Problems ever!!!!
84 230E Euro sedan [2 & 1/2 years ownership]
82 GMC Jimmy 6.2L Diesel [ 2 years ownership ] No problems
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