300D Electric window problems - PeachParts Mercedes-Benz Forum

Dave Billings · #1 04-08-2008, 11:18 PM

I have a 1982 300D and the right front and left rear windows don't work. There is 12 volts at the switches and one of the switches have been replaced. Any idea what might be wrong besides both motors being bad? Is there anything else I can check?

85300DT · #2 04-08-2008, 11:34 PM

Is the master lock out button depressed? Try taking out the switches and spray some contact cleaner in them. Re-install. If there is 12v leaving the switch, then check to see if 12v is hitting the motor. If no short or ground issue, then the motor is kaput..

cdplayer · #3 04-09-2008, 12:30 AM

Quote:

Originally Posted by Dave Billings

I have a 1982 300D and the right front and left rear windows don't work. There is 12 volts at the switches and one of the switches have been replaced. Any idea what might be wrong besides both motors being bad? Is there anything else I can check?

If you are still having problems, check the fuses carefully. Brass fuses are best. Less residue build up. I do not have a chart handy for your year and model, but just for reference sake, a 240D fuse chart shows the right front and left rear window's fuse is in slot "A". Left front and right rear window's fuse is in slot "B" in your fuse box.

tangofox007 · #4 04-09-2008, 10:45 AM

Quote:

Originally Posted by Dave Billings

There is 12 volts at the switches and one of the switches have been replaced.

How many terminals at each switch are showing system voltage?

LUVMBDiesels · #5 04-09-2008, 11:00 AM

Here is what you do.

*** If you have not changed the fuse do it before doing anything else.***

1) Remove the door panel from the offending door. it is very easy to do. You remove the chrome piece by the door latch, take a few screws out and pull the panel up and off. There are detialed instructions on the site search for door panel removal.

2) Look at the screw terminals attaching the wires from the switch to the motor. Remove the wires.

3) attach one of the motor wires to a known good ground

4) attach the other motor wire to a good 12v source (a jumper from the + terminal on the battery is good) The motor should turn. reverse your wires and the motor should go the other way. If this works the issue is wiring. If not, you have a bad motor.

5) If the motor works, check the wires coming from the switch. They should BOTH have 12V on them. If you press the switch to "up" one wire should still have 12V and the other should be grounded. the opposite is true when you press "down"

if you need to change your motors you need to remove the regulators. there are I think four nuts holding the regulator in. Remove them. Carefully take out the regulator being careful not to snap the plastic piece that runs in the track. Remove and replace the motor. carefully put the regulator back in. The window is free without the regulator, so be careful not to let it drop...

I would recommend doing searches on all the steps I just outlined. There are many posts detailing what I just said.

Good luck!

tangofox007 · #6 04-09-2008, 11:06 AM

Quote:

Originally Posted by LUVMBDiesels

1) Remove the door panel from the offending door. it is very easy to do.

It's a lot easier to troubleshoot the motor from the switch connector. There is no need to remove the door panels.

Diesel911 · #7 04-09-2008, 11:24 AM

When you check the fuses be sure to do more than a visual inspecion. (I had the same window problem but passanger side fron the driver side rear window not worikng.)
This is what was causing the problem with my windows:

Viewed from the front of the fuse box the fuses looked good. After finding this I pulled all the fuses and cleaned the terminals.

LUVMBDiesels · #8 04-09-2008, 12:11 PM

Quote:

Originally Posted by tangofox007

It's a lot easier to troubleshoot the motor from the switch connector. There is no need to remove the door panels.

Unless the wires going through the door jambs are broken. Happened to me. That is why I would go right to the motor wires.
Taking the panel off should be a five minute task.

tangofox007 · #9 04-09-2008, 12:59 PM

Quote:

Originally Posted by LUVMBDiesels

Unless the wires going through the door jambs are broken. Happened to me. That is why I would go right to the motor wires.

One the rear door, the wires connected to the motor terminate at the door switch. As long as you have system voltage at the switch, which the OP says he does, you can jumper the switch connector to operate the motor.

Quote:

Originally Posted by LUVMBDiesels

Taking the panel off should be a five minute task.

Checking the wiring for continuity at the switch will identify a broken wire in less time than it takes to pick up a screwdriver. And you won't damage your door panels or disturb the waterproof covers in the process.

LUVMBDiesels · #10 04-09-2008, 01:02 PM

Is the wiring different bewteen the 300D and the SD? My experience is with the SD where the wires terminate at a block inside the door. Maybe I am talking out of my hat

Jeremy5848 · #11 04-09-2008, 01:14 PM

The fact (stated in post #1) that a diagonal pair of windows doesn't work strongly points to the fuse or the wiring from the fuse block to the switches. A corroded fuse (as shown in one of the posts) or partiall broken wire can allow a few electrons to pass, enough to make a voltmeter register but not enough to operate the window motors. Always check the fuses first. The copper (brass?) fuses are generally considered better than the aluminum ones.

If that seems to be OK, then pull the left rear door panel (easier than the front, IMHO) and connect +/- 12 volts directly to the window motor (disconnect its wires first). The motor is not grounded. One polarity will make the motor go down; reversing it will bring the motor back up. If it's not the motor, try swapping switches in the rear doors. The switches can be taken apart and cleaned, BTW.

The motors themselves almost never fail. It's almost always a fuse, a switch, or the wires, especially where they go through the rubber cuff between the B-pillar and the rear doors and get bent back and forth every time the door opens and closes.

Jeremy

Dave Billings · #12 04-09-2008, 11:29 PM

Thanks for the help. The fuse was the problem. Even though there was 12Volts at the switches and the fuse wasn't burned out, the end of it was corroded which didn't allow full power through. Thanks again for all the help.

Quote:

Originally Posted by Diesel911

When you check the fuses be sure to do more than a visual inspecion. (I had the same window problem but passanger side fron the driver side rear window not worikng.)
This is what was causing the problem with my windows:

Viewed from the front of the fuse box the fuses looked good. After finding this I pulled all the fuses and cleaned the terminals.

jbach36 · #13 04-10-2008, 07:40 PM

Even if they look good, if you have the old fuses, pitch them, get the newer brass ones. The older ones can build up resistance, and cause electrical problems.

jeff