only the front windows???? (300SD)

[jimmy hat]

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

[Brian Carlton]

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.

[dmorrison]

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

[jimmy hat]

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.

[jimmy hat]

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!

[Brian Carlton]

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.

[jimmy hat]

sure. but aren't both the leads at the motor power leads. meaning the motor is grounded through its own chassis and the bolted connection to the steel door? maybe i am wrong, but, with my test light, i got power at both leads. the light its self is not powered, it only "lights" when one termial is grounded and the other is hitting a powered source. just want to make sure, because i don't want to cook the motor

[Eric Eliel]

On my 300D you can temporarily plug the front window female plug into a rear male switch to test the circuit. You said you have a known good set of rear switches. Test the circuit with the known good switches. My experience has been that the contacts on the V-shaped hardware inside the switch wear to a point where there is an inadequate electrical connection.

I have found the motors almost indestructable.

If you can hear groaning and movement, then you most likely have some broken/bent parts inside the door panel that must be attended to.

[Brian Carlton]

Originally Posted by jimmy hat

sure. but aren't both the leads at the motor power leads. meaning the motor is grounded through its own chassis and the bolted connection to the steel door? maybe i am wrong, but, with my test light, i got power at both leads. the light its self is not powered, it only "lights" when one termial is grounded and the other is hitting a powered source. just want to make sure, because i don't want to cook the motor

Negative. The motor is not grounded through its own chassis. The motor leads require one positive 12V and one ground for the motor to operate. The switch performs this function if it is working properly.

You may get 12V at both motor leads when the switch is in the neutral position. However, for the motor to move the window, one lead must be at 12V and the other lead must be at ground.

You will not cook the motor. Just make sure that the ignition is off.
Double check to make sure you have no power at both those leads prior to performing the test, as described above.

[dmorrison]

Your switch is working corretly. That is a correct indication of the 12V power going to the terminals. In the 12V system the consol switch changes the positive and negative wires to determine up or down.
So its time to remove the regulator. The regulator is mounted with a couple of nuts and is attached with a slide at the bottom slide rail.
Once you have removed the regulator you can examine it for electrical or physical problems. then testing it can be done with wire jumpers form the batter or a battery charger.

http://catalog.eautopartscatalog.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1EN19TNJF1EN19TSDW&year=1982&make=MB&model=300-SD-002&category=O&part=Window+Regulator&appChassis=_any

Dave

[Richard Eldridge]

My right front window, one fine day began to do exactly what yours does: when I push the switch, the other lights dimmed slightly and the window would not budge.

I took the motor out and replaced it. To do this, you will need to unsolder and resolder it, if it's like my wagon.

Before I unsoldered the motor, I greased all the sliders and checked all the parts to make sure that nothing was bent or wedged. When I replaced the motor, everything worked just fine.

When I applied 12 Volts to the old motor (from a 500 milliamp transformer), it turned slowly-much more slowly than the new one did (I tested it, too). I suppose that the motor could be repaired with some special tools, but I have not tried this.

It is unlikely that BOTH windows have defective motors, but it is possible.

Prices vary HUGELY for replacement motors, as I recall from $77 to $230 each, for the same new Bosch -made motor. I picked the cheapest one.

In any event, good luck.

[dmorrison]

Originally Posted by Richard Eldridge

It is unlikely that BOTH windows have defective motors, but it is possible.

I do agree BUT my daughters 240D rear window regulators were warped in the exact same way. I could have been a broken switch that kept power to the motor. Or a habit pattern with the previous owner. I don't know but I R+R both units and they seemed to have the same kind of failure.

Dave

[ajohnson1]

I recently had to replace the regulator on my drivers-side, I purchased a used regulator and motor assembly from James Harris on the Mercedes List for $33, (www.mercedeslist.com for info on joining). It was a used but very good condition, and I only needed the regulator.

His email is: h16671836_at_yahoo.com (replace _at_ with @, don't want James getting un-requested spam). You can try him to see if he has others.

Regards,
Adam

[jimmy hat]

okay more info.

when bringing leads from battery and switching placement of leads on motor connections, i get nothing... well not nothing. the leads basically solder themselves to the screws. big sparks zzzz zzzz and the wire tips a blackened. this happens instantly regardless of which lead is where.

i get no groaning, humming, any noise or movement of any kind when using switches, battery, nothing.

switches are good to go.

as far as removing motor and windor regulator: according to the service manual, i need to lower the window to do it, but i can't lower the window, and thuse the cycle begins. does anyone have a nifty trick?

thanks for the input, keep it coming.... i just wish my problems stopped there

[jimmy hat]

Originally Posted by dmorrison

Your switch is working corretly....
http://catalog.eautopartscatalog.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1EN19TNJF1EN19TSDW&year=1982&make=MB&model=300-SD-002&category=O&part=Window+Regulator&appChassis=_any

Dave

oh dear god dave, i hope i don't need the regulator...i can't afford that thing!