I have done two of these, one I managed to remove the 2 screws that hold the motor to the gear head (leaving the gear head in place) and then rotating the motor so the shaft unscrewed from the gear in the head. The other one I removed all the mounting bolts and then had to hold up the window an carfully push the bolts out and lower the entire assembly down to where I could seperate the parts. I think the first way was easier. It was not easy to get the 2 screws that hold the motor out but eventually I got it. Remember that if you take the motor out then there will be no resistance holding the window up and it will drop down.

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1983 300SD
200000miles

All right, I disconnected the two wires from the motor that connect to the door. Then I took voltage readings in a couple of ways. I put the probes both on the posts and got +13.8 in one switch position and -13.8 in the opposite position and 0 with the switch in nuetral. When I put one probe on one post and one to metal on the door, I get a reading in one position and not in the other with each post.

This makes me think that each of these wires is the hot side and the ground is the door. Comments welcome.

I was under the impression that depending on what way you wanted the window to go the switch just reversed polarity. If you test from the terminal to ground you still should get a complete circuit but only on the wire that is activated at that time.

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1983 300SD
200000miles

It's a strange deal. Both wires are hot when the switch is open. When the switch closes in one direction, the switch takes away the 12V from one wire and grounds it. When the switch closes in the opposite direction, it takes the 12V away from the second wire and grounds that.

It's all done in the switch.

I have had all my motors of all my MBs (wifs, sons and I) nonoperational at one time or another. After checking everything else and narrowing it down to the motor I found a neat trick to get the motor working again. (no doubt from this forum)

Most window motors were "frozen" due to rust issue in the shaft area.

Fill the motor body with ATF (yes it will leak all over you). use vice grips to move the shaft around. Then using a battey, jumper the motor to run in one direction.
Then reverse the battry leads to the window motor to run the motor in the other direction.
Only do this for a few seconds in either direction. Without any load the motor will spin like a tasmanian devil + burn out if run as such too long.

The ATF will lubricate the shaft/motor. All things being OK -your window motor is ready to re install and operate