My 300SD has had the right front-left rear window inoperable since I purchased it. I checked the appropriate fuse even replaced as suggested. Still no response. Pulled cover off passenger door and found 12V getting to motor so I pulled it out and tried to salvage with no luck.

Bit the bullet and bought a new motor (from CarQuest no less at $125). Tested it before mounting and worked as you would expect.

When I put it in and reconnected wires - Nothing !. Pulled wired off and checked voltage, now its around 10.5V. Replaced fuse again, pulled window switch out (as suggested) and cleaned it. Voltage back to 12V+. Put it all back toogether again and still the motor won't run mounted in door.

What's going on? I saw mention of relays in fuse box area and two of the four in the area are very hot after leaving ignition on accessory for a while to test. Are they somehow possibly involved?

Any suggestions would be appreciated.

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83 300SD 280K
78 240D 200K+ sold 10/07
94 BMW 740IL 220K

It's also common for a wire to become broken between the door (tunnel) and the "A" pillar. Do a continuity test between wires at switch and wires to motor.

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BENZ THERE DONE THAThttp://www.peachparts.com/shopforum/...c/progress.gif
15 VW Passat TDI
00 E420
98 E300 DT
97 E420 Donor Car - NEED PARTS? PM ME!
97 S500
97 E300D
86 Holden Jackaroo Turbo D
86 300SDL
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Sorry to sound like a dummy but what is the "A" pillar. I know where the tunnel is that gets the wires routed into the door cavity.

Thanks for the suggestion

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83 300SD 280K
78 240D 200K+ sold 10/07
94 BMW 740IL 220K

you might try running some jumper wires from the switch to the motor bypassing the wire harness in the car. even though you are getting 12V at the motor, a frayed wire will not give you enough amps to move the motor. with a jumper you can verify the switch and the motor which leaves only the harness between them as the failure.

also, the switches can be plugged in wrong. did you hav ethe switch unplugged for any reason witout marking the connector locations?

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1982 300CD Turbo (Otis, "ups & downs") parts for sale
2003 TJ with Hemi (to go anywhere, quickly) sold
2001 Excursion Powerstroke (to go dependably)
1970 Mustang 428SCJ (to go fast)
1962 Corvette LS1 (to go in style)
2001 Schwinn Grape Krate 10spd (if all else fails)

I will do the jumper business to see where the "villian" area might be.

I did unplug the switch and replug but only after the troubleshooting began. The switch seemed to be "keyed" to not allow much chance for error. Am I overlooking something?

Also using the switch and the motor "unmounted" sometimes resulted in the motor working

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83 300SD 280K
78 240D 200K+ sold 10/07
94 BMW 740IL 220K

Door Frame (hindged side).

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BENZ THERE DONE THAThttp://www.peachparts.com/shopforum/...c/progress.gif
15 VW Passat TDI
00 E420
98 E300 DT
97 E420 Donor Car - NEED PARTS? PM ME!
97 S500
97 E300D
86 Holden Jackaroo Turbo D
86 300SDL
(o\|/o)

It is fairly common for the wires to seperate at the door hinge area. This will happen with out seperating the insulation. Does the window motor work either with the door open or with it closed. Another point is the polarity of the wires to the motor reverse depending if you are raising or lowering the window, Try reversing the wires at the block in the door and then test. As suggested run a jumper from the battery to the motor, this will tell you if everything is ok at the motor and gear head. Run the jumpers to the block in the lower left of the picture and try it with the wires both ways.

Attached Thumbnails

 

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1983 300SD
200000miles

Thanks to all for the ideas, but here's what the problem turned out to be.

I traced all the window power wires and jumpered it at the various points all the way back to the switch and all worked OK.

I had taken the advice of the group and replaced the appropriate fuse for the passenger and left rear door. but any load on the circuit drew the volts way down until I wiggled the fuse in the socket.

Last resort, replaced the fuse AGAIN. Things worked !!! Don't suspect new fuses to be flakey

Only saving garce, the passenger motor was indeed bad as well.

Hope this helps someone else !!

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83 300SD 280K
78 240D 200K+ sold 10/07
94 BMW 740IL 220K