'81 240D Power Windows Short (?)
 

Hi! I just bought a beautiful cream-colored 240D, 139,000 original miles, and while I was fixing a buzzing in the hazard light (I spilt water on it but did fix the buzzing) the wires that connect to the right rear power window switch came out of their protective box and a couple of them touched and brightly sparked. I must have had the power on to test the hazard light when this happened. After putting everything back the way I found it the right front power window switch sent the right rear window down halfway (I may have had the four right rear window wires configured incorrectly at this point, but they should be right now) and now all four windows cannot be controlled by any of the window switches. They are stuck where they are. The fuses seem to be okay, the turn signals and hazard light work fine, do any of you have any ideas of what I can try replacing or adjusting to fix this issue? I know there is a power window relay behind the dash. I was really bummed to have caused some maybe complicated harm after a long day and a successful fix. Any advice is greatly appreciated! It's hot out here ….

As far as I know there is no power window relay
under the dash. Recheck the fuses. If you still have aluminum fuses replace with copper fuses.

Thanks for your reply, fuses are double checked and copper. The box directory does actually mention a power window relay, given the sparking could this be the issue? If there is a relay could that be what was spent by the sparking?

You will need a test light or a cheap digital meter. To check for the supply voltage etc. There are two electrical circuits for the windows I believe. One circuit does one front door and one back door. The other circuit does the other front door and the other back door.


It may be helpful for you to get a wiring diagram. If there are two fuses for the window circuit you know you have the dual circuits.


I also could be wrong about my description of the electrical setup. Others will correct that if I am. Just as a guess it sounds like you may still have some wiring connections mixed up. If you have no electrical experience and it where possible to look at the connection order of another car I might take advantage of that. Even one in a wrecking yard. I had a quick look at a manual.

There are two window lift relays present in the wiring diagram .I just looked at for the wiring in the north American 123 models. plus there are two circuits as I described. I assume it is the six wire plug that became partially disconnected? Post the year of your 240d so I can go over the specific wiring diagram. They all probably are the same in this area but stupid to ignore that they may have made some changes over the years. I doubt you have done any serious damage by the way. I or someone else may be able to make a suggestion.

Thanks for this! I actually have an 85 300D that I have yet to get rid of that's good for parts. My 240 is a 1981. I'll send a picture of the wiring later, the wires that got excited were from a 4-pin. I'll also try and find photos online this evening for wire color reference to check that all is connected correctly.

The power window relay uses a separate fuse that is shared by some other components. On my 84 300D that is fuse #12. Look at your fuse chart to see where yours is.

I have noticed that in at least the last 3 years W123 owners ask questions here by seem to have no use for the Factory Service Manual. Notice that in this case the Factory Service Manual would have had the info on which sockets the wires were supposed to go in.

Diesel911 good point I will definitely pick one up. I had one for my 300 up until a few months ago when I misplaced it. Thanks for pointing this out!

I found this website that provides instructions on how to access cd-romantic format factory service manuals hosted online. I'll take a look later but though I'd share if it's a helpful tool for anyone else. I didn't know this existed.

https://blog.*******.com/using-free-service-manuals-for-mercedes-benz-w123-and-w124-models

replace asterisks with *******

with f c p e u r o , no spaces

I found a factory service wiring diagram and all connections and fuse box fuses seem to be in order. Thanks for this suggestion, it was a satisfying to figure out how to check the wiring from a diagram. I'm stumped. As for the voltmeter and circuits, where should I be putting the positive and negative ends of the voltmeter to test, and what am I looking for? I've been using the factory service diagrams from startekinfo.com. My 240D is an '81. Oh, and not knowing too much about electricity, when the wires for the right rear window touched and spark/popped, where would this go/what would this do? I would imagine it would go straight to the fuse box and pop a fuse, but this doesn't seem to be the case.

Thanks!
A