94 e320 rear dome light issue
 

don't know where to start troubleshooting really, so any help would be appreciated. rear dome light does not turn on when open a rear door or with dash switch. it only barely goes on when the truck is open, not sure if it is supposed to do that at all. the following maybe be tied to this ... sun roof doesn't work so i unplugged it, power antenna doesn't work either ... the dash rear light switch does however turn on the lower lights that are on the bottom part of the rear doors. these have been like this since i bought the car a few yrs ago

Ok let me please ask this to you fellow w124 sedan owners. Does your rear dome light turn on when you open your trunk?

Interesting. Any time I have issues like this I usually suspect a bad connection somewhere.

Here's where I'd look in order:
1. Fuse box under hood. If any fuses are not the newer style brass metal type, replace them. Also inspect for any corrosion. Also, take a fine sandpaper and clean the contacts where the fuses connect in the box.

2. The grounds for the light. and make sure they're referenced to the chassis ground near battery ground.

3. The switch above the CCU push buttons.

Many electrical problems in these cars come from problem number one.

thanx for the reply and for the starting point to my troubleshooting .... I wouldn't be surprised if it was a simple fuse issue as some of them look very old and repaired/soldered instead of being properly replaced.

It might also be a ground issue as I remember when I got the car, every time you would start the car, the sunroof moved a little on its own. This caused the sunroof to go down little by little over a few days period. I eventually used the manual override for the sunroof through the trunk and shut it completely then unplugged it til I could find the issue.

fuse for rear dome light is ok. rolled it around in its place a little plus checked its contacts for corrosion, but it was clean. I do however hear a relay click (possibly the convenience relay behind the fuse box) the moment I put the fuse back in its place. not sure if that is supposed to happen. I'm starting to think convenience control module (CCM) is at fault. sunroof and auto antenna both don't work. Not sure if my car came with the auto windows down/up feature that when out of car can open all windows or close all windows with key on driver door lock. if my car came with that feature it doesn't work. I think i have MB tex seats (and the car may be a base model) so I probably don't have that auto down/up windows feature ... the auto down for passenger front window from the window switch works perfectly. the auto down for driver front window from the window switch makes the window only go down half way, then i manually hold the button down to make window go all the way down ... I believe all of these are through the CCM

update ... did more troubleshooting, the relay that clicks when i put fuse c back is the power seat relay, don't think its supposed to do that. Also removed fuse c to test voltage and its only 6 volts

I dont wanna seem odd but have you tried replacing the bulb or checking for voltage at the bulb socket?

thats not odd, the voltage readings i get are odd lol .... I was going to replace the bulb yesterday, but tried out so many scenarios it confused me more. I believe with the trunk bulb plugged in I get 6 volts to the rear dome light. Now the trunk bulb is unplugged and I get something like 0.17 I can't remember. I was so confused, I gave up but maybe during the week I can write down my findings. However, the back door lights at the bottom are both almost 12 v and so are both of the back door switch voltage readings. Just gotta keep searching with the wiring diagrams I guess to see where the PO messed with the wiring. (I'm still not sure if a bad convenience control module which is under the back seat would cause these symptoms.) I did however see that the sunroof power wire is almost 12 v, but the antenna power wire is something like 0.17 or 0.18 with the convenience relay removed or swapped with the power seat relay.

not really a great update, but i'll post any way ... i got a replacement comfort module (under left side of rear seat) and sunroof works now ... i also right away tested the feature that closes open windows and open sunroof from outside of drivers door with key held in lock position and it automatically closed windows and sunroof about 5 times in a row flawlessly ... had to show family (as this never worked in all the years i had the car) .... however went for a drive tried it again and no go seems replacement comfort module got fried too ... i found that rear dome light had a constant 12 v with all the doors closed and 1.18 volts with any rear door open (possibly both ways opposite polarity too) ... (same voltage readings at dashboard switch connector for rear dome light) i have since disconnected connector E from comfort module and it seems to have made volts at rear dome light about 0 to 0.5 v all the time .... i have rear dome light connectors in place but no bulb, also no bulb in trunk light, and also disconnected rear trunk light switch ... I figured out that sunroof now works the same if comfort module has all its connections or none at all ... I have now also lost the one touch window down feature of driver and passenger front windows that worked with previous bad comfort module connected ... another owner of a 94 e320 on this site noticed that he had trunk light wires that had become wired to each other possibly from heat and this caused his comfort relay to go bad, that is what i figured happened in my car and thats why i am trying all i can to get the trunk and rear dome lamps out of the circuit ... any one have a complete wiring diagram for the comfort module?

please see attached photo I found online .... only difference is my E connector has red/white, brown/violet, black/yellow wires only ... this one looks like it also has a violet wire there which is missing from mine. don't know if thats another option or if previous owner disconnected that (and this is my issue)

I had almost the same problem with my E420. Most likely your wires are fired together like mine were in the rear of the car. I had to rewire everything from the Convience Comfort Unit under the rear seat to the trunk. Take the time and expose the wires that runs on the driverside rear deck to the trunk. Im sure you will discover that the wires that runs to the trunk light, rear interior roof light, tail lights and power antenna will all be fired. Mine was so bad that it keep burning out a fuse before my eyes. It will take a while but take your time and cutout all the bad fired wire and replace it with new wire. Dont take any chance by trying to use the bad wire at all, save yourself the headache and just cut it out. After running new wire to the trunk light and etc.. your E will be as good as new with no electrical issues.

In addition, you will need to buy another Convience Control Unit because most likely your circuit board inside is fried.

Good luck!

thanx so much man for further proving my theory ... I was worried it would come down to this, but it sounds like my project for the summer