1992 300DT electrical issue?
 

Systems in the car have been slowly failing over the last year. Recently the windows, sunroof, and windshield wiper stopped working, as well as some of the power seats/headrests. I just replaced the control module under the backseat, this usually solves these issues I've read. For a second, I had windows that worked! Then....nothing. Again. Any Ideas? No heater blower, no working windows, no wiper. Car starts, and moves under its own power, headlights, taillights, turn signals all work. Not currently driving it, as I don't know what the problem is. Any help would be appreciated.

W124 cars have several grounding points. Check em and clean em

Thanks for that advice. Ummm, novice here...where would those grounding points be located?

Check the fuses with a test light make sure they are working sometimes they have corrosion specially if the car has been sitting a long time

Sorry, but I don't have a W124. However, MB uses similar grounding procedures across many models. Also, it may take longer than usual to get responses to your question due to the holiday week. Many forum members are traveling, with family and friends, etc.
Since you're unfamiliar, and there's nothing wrong with that, we all "start" somewhere, do a quick search for "W124 ground points". You'll get a bunch of hits and ideas about what and where to look on your car.
This might be a helpful link: https://www.ifixit.com/Guide/How+to+clean+Mercedes+W123+Electric+Ground+contacts/20580 The poster has a bunch of well done (IMHO) MB maintenance and repair videos.

A lot of the ground points are a small bundle of wires with brown insulation. They're stacked onto a stud and bolted in place. Again, lots of pics on the net. Remove the bolt and washer (using care to not drop it as it might disappear somewhere) pull the wires off, then clean all the parts. Cleaning means with abrasion, not fluid. Scotch-brite or emory cloth works well. Dont use anything too rough. Just trying to clean up the surface. Be gentle with the wire terminals as you don't want to pull any of those off. You also may find corroded wires and replacement terminals may be in order. As always, make sure your main battery terminals are both clean and tight. Not trying to "talk down" to you. It's just too easy to assume someone knows what you're talking about when they might need more info. Trying to be clear.

I know you wanna get your car going/fixed asap, but take your time. You'll learn a lot in the process and hopefully won't have any "setbacks". you may be able to find a link that shows most of the ground points on the car. They're, literally, all over the place.

This forum is the "place to be". Tons of highly experienced members. You'll get your answers eventually. As I mentioned, this week and next week will have a lot of people "out of the loop", so to speak.

Don't be afraid to ask questions or request clarification. No one will hold that against you, here.

This X's 1,000....

You guys are awesome. I do have another vehicle, so not in to much of a hurry, altho I've been using this car to teach my grandson to drive, and he misses it,lol. Time to do some google sleuthing about those ground points!

w124-zone was a well known resource for w124 fsm. has recently had some hosting changes but all the info is still here.

google w124-zone and you can find a link the new hosting site