1992 500E 132,000 mi. Charcol Grey. It's a full moon tonight.

Loving the car so far except for fact I can't see my dash at night..

Scanned lots of threads and have run lots of searches. I downloaded the schematics from braingear and they have been quite helpful.. BUT.. man.. I just don't know if I'm doing enough when 'eliminating' a curcuit as the culprit.

SYMPTOMS:
Turn on running/head lights and fuse #3 (cuircuit 58R). Fuse box shows it covers:
parking/tail light right
headlamp cleaning unit
warning buzzer
illumination: license plate, instrument, control elements

Otherwise not other electrical or performance issues.

CAR:
Stock as far as I know (I've had it home for about 8 hours now). Factory Becker radio with MBZ badged CD changer in trunk (which is also not working.. perhaps this is a clue as well). Radio works fine. Wiring harness are stiff but do not seem 'brittle' in the trunk area.

DIAGNOSTIC SO FAR:
- Lots of fuses tossed at this, all of them burned up.
- Unplugged both right side parking/tail lights. Flipped headlamp swith to the parked mode (one side of car illuminated only). Fuse was OK. Plugged lights back in and it still worked (both front/rear illuminated).
- Unplugged headlamp wiper relay (D on diagram) - fuse still blew.

I'm thinking the next stop is to check the wiring into the trunk area (going after the low hanging fruit first). What is the best way to really check this for problems? I have it out of the harness holders but I have not split the extruded loom or cut into the black insulation around the 3 wires into trunk lid. Should I remove the liner on lid, cut wire and pull it through the trunk support stip it all back and look for shorts? I'm OK with doing that if it's the best/only way. If there is some easier less invasive way to do this I'm all ears.

If this does not work I'm going to try to pull the inst cluster (done this on my 300 before, not fun but I know the drill) and see if there is a way to unplug all of it and eliminate it from the possible cause. Maybe the regulator on the back of it (does it have one?) is shorted?

Having the door open or closed does not have an benefit. Fuse still blows, only diff is that if the door is open I hear the buzzer for a split second as the fuse burns up.

Is there other wiring (the diagram is 274 pages and I'll admit I've not read all of it yet, still trying to decifer the way it references the next sheet on a wire run) that I need to unplug or (cut??) to fully eliminate the headlamp wiper motor system as the cause? I'm thinking that pulling the relay is not the full solution but it was the quickest to try.

Help?

I'll keep searching the archives and if I find something that I think will work (or does work) before there is a reply I'll post such.

TIA!!

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BUMMER - NOT FIXED

I cut the 4 wires to the trunk wiring and VIOLA. Fuse is holding. I'll return the wiper motor module to relay box and see if that causes it to blow but it looks like the problem is somewhere in the trunk wiring harness. This.. I know I can fix. WHERE the problem lies I do not know. It was a cude method of diagnostics but at least I have it isolated.

Unless I'd read the multiple threads about the trunk wiring being a common failure point I don't think I'd have cut these wires as a diagnostic step! LOL. When I find the final problem (broken, stripped, crushed wires) I'll post an update. YES! It did not turn into a major car teardown!!!

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Thought I had it fixed but it blew again today. I still think it is trunk related since I was able to put in a fuse, turn on the lights and everything was OK until I slamed closed the trun (it's always required a bit of effort to close). It did this twice. Everything fine until I closed the trunk.

Now, it blows every time I put in the fuse and turn on the parking/head lamps.

It's still OK if I just run either the RIGHT or LEFT standing lamps (markers only) but when the inst/license/interior lights are in play.. POOF.

I don't know if this is normal but when I test continuity on the Grey/Viloet and Grey/Viloet/White wires (these power the license lights in the trunk, they are still cut-off at at the loom) they show only bout .06 ohm resistance to ground. This seems very wrong to me. I'm assuming this indicates there is a short forward of the bend in trunk wires.

ANY diagnostic suggestions/tips/hints are appreciated. HELP!?!

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That resistance you see (.06 ohm) could be the lic plate bulbs. Pull the bulbs and check to see if your power wires are still going to ground. If yes, you've got a short there.

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Fourings

84 Audi Coupe GT with Turbo engine, EFI (buh-bye CIS), Jamex seats, Koni's/H&R's, e-code lights. 210k and counting.
1992 Anthracite 400E, 161k, "Grey Ghost".
1986 VW Quantum Syncro, 192k, gone to the crusher in the sky.
1989 300TE 172k. (Was mine, now also Mom's car)
72 280SE 4.5 (Mom's car)

Bulbs are cutoff from the curcit. The 4 wires to the trunk are still cut so what I'm reading is the value on the harness going towards the front of the car.

I've looked at the wire diagram and it *looks* like these two wires go direcdtly to the Lamp Out module, but I wonder if they also T-off to the inst cluster. There are only 247 pages of diagrams so.. maybe I missed a page? I'm looking at page 126 where it shows the two wires in question (GY/VI & GY/VI/WT) going to the rear. The low resistance seems very odd. Would that be from the module or are those two the culprit wires I wonder.. (but why would both be sorted.. seems odd).

I don't suspect the inst cluster or the control illumination because it seems to work OK when the fuse does not blow.. (then again.. who knows..). It's just really annoying to try and drive at nigth with no inst and only 1/2 of my marker lamps..

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I'm not sure measuring resistance from the trunk harness forward to the switch is the best way to go about this. If you cap off the wires feeding the trunk so there is no chance they can touch each other or anything else when you close or slam the trunk you should be able to eliminate the lic plate lights as a cause.
The reason those two lights are fed seperately is so your lamp out module knows by comparison if one is out.
You could also have something going on with your instr cluster lighting. Dash lights don't come on with the curb lights. The fact that your curb lights don't blow the fuse is probably an important clue.

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Fourings

84 Audi Coupe GT with Turbo engine, EFI (buh-bye CIS), Jamex seats, Koni's/H&R's, e-code lights. 210k and counting.
1992 Anthracite 400E, 161k, "Grey Ghost".
1986 VW Quantum Syncro, 192k, gone to the crusher in the sky.
1989 300TE 172k. (Was mine, now also Mom's car)
72 280SE 4.5 (Mom's car)

That is my concern, that I'm chasing a red herring on those two wires.

I considered that. The only reason I've not looked there yet is everything seems to be related to opening/closing the trunk, so I *thought* it was the wriing to the license lights. Not so it would appear. Movement of the harness back there as the next cause I wanted to eliminate but.. ripping into harnesses trying to find the elusive short is just frustrating me and ripping up the car, neither I find very successful (or gratifying).

I just thought (DUH) I have another W124 body here that I could start checking to see if those wires show a similar resistance on a circuit that I know works.

At this point I'm literaly shooting in the dark..

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You could be on to something with the trunk, but it may depend on where you cut the wires to the trunk. Wires being bent back and forth like at a trunk hinge, or a door hinge will eventually break. Sometimes causing a short, sometimes just cutting power or ground. My 300TE had this happen. Depending on where you cut the trunk harness, you may still have a short between the trunk area and the fuse. You may have to open up the harness wrap right where it bends when the trunk opens and closes.

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Fourings

84 Audi Coupe GT with Turbo engine, EFI (buh-bye CIS), Jamex seats, Koni's/H&R's, e-code lights. 210k and counting.
1992 Anthracite 400E, 161k, "Grey Ghost".
1986 VW Quantum Syncro, 192k, gone to the crusher in the sky.
1989 300TE 172k. (Was mine, now also Mom's car)
72 280SE 4.5 (Mom's car)

This is what it looks like right now...

Attached Thumbnails

 

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OK, this car has transported into the twilight zone. In the photo in my previous post, lower left you can see three sets of ground wires bolted to the frame. Just for kicks... I removed them and checked a new fuse.

No short!

UPDATE After a LOT of ripping wires out of harnesses and checking for crushes, pinches and other damage, I found nothing. Nothing at all. I did narrow it down to just one of the ground wires that when re-attached blew the fues. Oddly this one supports the tail lights.

What I noticed tonight was the my standing lights diagnostics (left only/right only) was not as full as I had though. What does not come on in the reaer are the small side markers. It turns out that the left (not the right which is what the circuit is supposed to protect) will blow the cicuit if I place a lamp in there. So I re-taped, wrapped, and protected the harnesses again, replaced all the panels and re-grounded that last wire and left the two side markers out. Then slammed the trunk numberous times and took a nearly 100 miles drive in the wet on the bumpy rounds in the shoud county. All still working just fine. I don't know why that single lamp blows it out but it does. Why the corner lamp on the right side does not blow it out is very mysterious. There is still a fair amount of harness I did not shred (I stopped when I discovered this bulb thing). So it's onto more wiring research to see what else might be connected to that set of wires. Baffling.. but at least I have lights for night driving again.

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What is history of car? How long have you owned it? Where did you get it. The reason I ask is that several years ago a guy called my shop with a similar problem. It seems he got a smokin deal on an S class at a car auction. The trouble was that he soon found out that the car had been hamburgered together from a major rear ender and dumped at the auction. I don't know what the guy ever did, because nobody in the profession wanted to touch the car. Hopefully this isn't your case.


MBs do not ever have wiring issues so you probably need to take the car to a professional before you destroy the car.

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Auto Zentral Ltd.

I was afraid of that so I had a CARFAX run (hardly accurate, I know of one car we had that suffered 12,000 in damage requiring a complet right side replacement that did not show up on CARFAX) and it was clean.

I've removed all the interior panels in the rear and I see no indication of any damage, welding, filling etc. I'll have to check the front panels for the factory serial numbers to be 100% sure they all match.

Yes, the last thing I want to do is shred this car considering it's one of the more prized of the W124s. For now, I will keep scanning threads to see if anyone else has found a similar issue. I suspected there was a pinched wire between the two tailight units but all the wiring looks good and no no-factory fasterners have been run into the body back there (classic cause of these things are hack-job installers running sheetrock screws into bodywork without checking to see if there are wires behind the metal).

Seems to OK right now. Of course it was OK for a bout 4 days last time and then suddenly popped a fuse again. Upside is that I was able to re-produce easily with that one wire which I put a paint mark on for furture ref.

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