Power Window Troubleshooting

When all else fails check the wiring

This problem is starting to show up more often as all these old Mercedes Benz age. If you have replaced other parts and are still having problems with the operation of one of your power windows, then you might want to check this, especially if the window is showing signs of intermittent operation. The problem occurs after countless hundreds of times of opening and closing the door. At some point the wiring bundle that goes from the door into the door post will become brittle and the wires will actually break. When the wires break they may only make contact when the door is closed. You may find when the door is open your window wont go up and down. Worse yet I've seen these wires on some occasions start cross connecting and blowing fuses. What makes this most frustrating is it can be very intermittent. Sometimes the windows will work, sometimes it will blow the fuse, sometimes it won't blow the fuse and you may be replacing window motors or switches and be totally frustrated because you can't find the problem.

Problem & Solution

Common among these chassis:

W108 W109

The problem can often be found in the wiring between the door and the door post. The wiring actually flexes in this area (when the door opens and closes) and will break over time. As you can see in this picture of a 201 chassis 190E all four wires were found clearly broken. For some reason this seems more common in the 190E's than in other chassis. But I have seen it show up in 123s and other chassis through the 80s and into the early 90s. Just be aware if you are experiencing weird sporadic power window failure and fuse failure then you might want to pull the door post covers and inspect this wiring.

NOTE: you will have to cut the braided installation back from the wires using a razor blade to inspect for breaks in the wire(s). To repair the problem you will need to remove the door panel and install new lengths of wire that you run from inside the door up through the door post section and splicing them down into the inside of the door post where there is no flex.