I have been driving my new 82 300SD around for a couple of days. Ive spent a lot of time working the bugs out. The front power windows aren't working. at first i thought it was the switches so i cleaned up several sets and tried them all. both the back windows worked with all switches, the fronts never worked with any switch. i am now positive the switches that are in the car are a working set. you can actually see the draw in the dimming of the dome light in both positions of both front switches. anyway, i am wondering if you guys can help me with the next step. i noticed when i had the driver door panel off there was a 2 screw terminal mounted near the lower right of the door. i think it was a green an black wire. they looked like they went to the power window motor. are these positive and negative leads? if i had a 12 volt drill battery, could i touch these terminals with leads from the battery pack and cause the window to go up or down depnding on polarity? just want to know what the next step in trouble shooting is. i never realized how terribly inconvenient it is not to be able to roll down your window. oh, and no blown fuses that i can see. please help

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1982 Mercedes 300 SD

Yes, you are entirely correct. You can attach 12V and ground to those leads and the window will go one way or the other. Reverse the leads and the window will go the opposite way. If you are quite sure the switches are operational, then you should get no response to the application of 12V and ground to the terminals. If you do get a response, and the motor works properly, check to see if the switch will send power and ground to those leads.

There is another possibility:

The electrical system is fine and the motors work fine, however, the regulator has a damaged plastic sliding piece that means the glass will not go up and down.

Do some additional checking as described herein and report back.

Couple of things to look at.

Check the power at the door terminals as you are thinking. The wires that go thru the door at the hinges can break after a 20 year life. So if you get no power there then you should check the wires at the door hinge.

2nd the actual mechanism can warp and not work. It jambs the mechanism and prevents it from working. My daughters car had this in the rear windows. the cast alluminum regulators were warped.

3rd The slide at the bottom of the mechinism can go bad and jamb. Thsi can be replaced but you must remove the regulator to do it.

4th The motor can fail but usually does not happen and if the lights are dimming then they are probably working, or at least drawing electricity.

5th With a schematic and a Ohm meter test the consol switches to make sure they are working correctly.

6th check the continuity between the consol switch wire harness and the terminals on the door.

Dave

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1970 220D, owned 1980-1990
1980 240D, owned 1990-1992
1982 300TD, owned 1992-1993
1986 300SDL, owned 1993-2004
1999 E300, owned 1999-2003
1982 300TD, 213,880mi, owned since Nov 18, 1991- Aug 4, 2010 SOLD
1988 560SL, 100,000mi, owned since 1995
1965 Mustang Fastback Mileage Unknown(My sons)
1983 240D, 176,000mi (My daughers) owned since 2004
2007 Honda Accord EX-L I4 auto, the new daily driver
1985 300D 264,000mi Son's new daily driver.(sold)
2008 Hyundai Tiberon. Daughters new car

sounds complicated. if the lights dim with the switch, i am guessing your suggestions about the motor actually drawing is correct. whcih means i have a jam in both front windows. it just seems odd that both front windows have the same problems, doesn't it? also with a jam would the window even "shift", like hint that it wanted to move? i will check it in the morning with the battery on the terminals. if it moves than i guess i have a bad wire, which is going to be a drag to track down. i will keep you guys updated, i am sure i will have more questions, thanks for the help.

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1982 Mercedes 300 SD

worked on the dirvers side a little today.
this is what i found: there are two screws at a plastic block mounted to the door. the screws connect the wires to the motor. when the key is in the acc position i have power at both screws (testing light grounded to regultor bolt). i have power at the motor too, at both wires. when i move the switch forward, i have power at the top screw (green) and nothing at the bottom screw (black). when i move the switch back, i have power at the black wire, nothing at the green. seems to make some sense although i have no idea why i have power at either screw, let alone both, when the switch is in its centered (unengaged) positon. hooking up a drill battery to either terminal (positive to screws, negative to ground) does nothing. no jarring or movement of any kind. i tried another set of known good switches. again only back windows, neither front. i also tried taping the switch in the down position and gently helping the window down. this did nothing. seems like the motor is seized, but i really have no idea what else it could be. i don't have a wiring diagram so i am not sure how to figure out when i should have power and where. hopefully you guys can't point me in the right direction... no idea what to do next, as far as i can tell, its not the switch or wiring... beyond that, i have no idea. please help!

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1982 Mercedes 300 SD

It appears that the motors may be bad. However, as previously mentioned, this is unlikely.

Can you please make the following test (because I have no confidence in a "drill battery"):

With the ignition switch in the off position:

Connect a test wire from the positive battery terminal to one of the terminals on the door.

Take a second test wire from the negative battery terminal and touch it to the second terminal on the door.

See if there is any response from the motor.

Reverse the wires to the terminals on the door. Touch the negative wire to the opposite terminal.

See if there is any response from the motor.

Report back.