need help with 1991 300e window switch
 

Does anyone know what might be the problem with my 1991 300e drivers side window switch. It intermittently works. I've changed out the original and still have the same problem. It will always open but will go up a third of the way and stop. I'll disengage the switch and it will go up another third of the way and so on. It only happens on this one switch.

I don't know exactly how the "convenience" feature works on these cars, but that is the first thing I would suspect. Are you able to close your windows and sunroof by locking the driver's door with the key from the outside and holding the key in the "lock" position? I'm not sure what year they started that. My 89 didn't have it, but my 92 does.
I saw the same thing happen on a Passat once with the same convenience type feature. Wound up replacing the window motor/regulator as the ECU was built into that. Somebody here will surely know what part is troubling you.

The 1990 & later USA W124 chassis has a computer for window/sunroof under the rear seat on left side. THAT is the place to start.

Dear M.B.Doc
 

I fear the aforementioned ECU is culprit for my problem, 92" 300E
W124 - 3.0 litre.
Is there a proper name/id. number for said part, & replacement options; ie; new, rebuilt, aftermarket? Best Where to purchase?

Thanks in advance for any helpful reply. Hanz

comfort control unit
 

Here's a pic of the unit from a W124. Found under the driverside rear passenger seat.