I just bought a 1985 300sd. When I bought it the previous owner explained that one of the rear windows didnt work. Upon getting it home, I found that all the windows worked. However, the next day, I lowered the drivers window, and now it will not go back up! There is no noise indicating the motor is attempting to raise the window... nothing! The other windows all still work, which seems to rule out a fuse issue as I understand it, the fuse is for more than 1 window, and all the others still work. Anyone with experience in this issue with a possible solution? Your assistance would be greatly appreciated! I can be reached here, or at brentetn@yahoo.com Thanks

 

common problem of the W126.

Now, if he motor is not turning and if at one point the prev owner said that the windows wasnt working and the window worked for a second, and now not working, the switch itself could be going out. To rule out switch, try unplugging the switch and and plugging a known good switch in it's place and see what happens. If the window operates normally then problem is found. If still no go, then the regulator might be starting to go. Before throwing that expensive part around, see if you can move the window up by hand from the down position. If so, the window is becoming misaligned and needs to be put back on track. If not, the window is still on track but dont force it out of track. The resistance should be minimal. If the window is off the track or is able to be pulled up by hand, move it to the raised postion and try to operate the window by pressing the up button as if tryoing to realign the motor position with the actual window position. If he motor kicks (will be faint motor sound becase no glass to move) roll it up to to position to match the glass. You might hear a slight thunk as the glass and motor meet up at proper place. At this point te window should not slide down on it's own. If you make t through all these steps that means the window regulaotr plastic slid jaw is shot. a 30 cent piece and a six pack to get to.
To get to it, you'll have to take the door panel off regardless and easier to observe also what exactly is going on with door panel off. and you'll see extaly what is slipping and the plastci little piece I'm talking about, one of the few plastic white peices of the power window assembly.
If the motor is not kicking at all or intimitt. regardless of conditon of switch, then first place is to check the wires of the motors and stuff, can easily be done with door panel off too and flashlight and sometimes a dental mirror. Also another way to rule out the switch is to take switch of suspected window and plug it into another working window and see what happen. From those steps you'll be able to tell whether if it's that plastic piece or the motor and dont worry if you on budget, plenty of window regulators can be found at scrap yards especially with the amount of poor perfectly working W126s that fell victim to the cash for clunker trend. Also yo can find rebuilt ones all the way for brand new ones. Not the most exspensive thing on the car either way you go about it unless you o to the dealership.
As far as the wor is concerned, it's not too labor intensive, slight time consuming and careful working condititions and a little finesse to change out the whole assembly. The plastic peice is a few curse words getting it out and even more getting it in but not toohard.