Mercedes made a rare boneheaded move in the engineering department for the 70s/80s designs.

It is a rule in industrial control panel design that you must have fine stranded wire when crossing a hinge point. For example, UL508A requires #14, 41 strand or #12, 65 strand when crossing the hinge.

The wiring looks to be standard stranding, not sure what the strand count is but it looks to be in the low double digits.

The only effective repair is to cut back the wiring to a point where it is not flexing, and solder/heat shrink splice in fine stranded wire of equivalent gauge.

Note that 124s with non-memory power seats have direct battery power going into the doors as these seat motor switches are directly switching battery power to the seat motors. These wires cross the hinge and if that shorts it will be ugly. There is a 25 A fuse but the clearing time on that fuse is rather long...:eek:

It makes me want to go inspect all 4 doors on my 124.

I'll see if I can find pictures of the work. As I recall, I patched in new pieces of 18-gauge stranded wire, soldering each end and using heat shrink tubing. The wire length was about a foot so that the ends were in the door and in the B-pillar and new stranded wire (only) was in the accordion.

Jeremy

Given the fact that I wouldn't be able to own these cars without all of your help, my tab shows a lot more than $0.02. Thanks guys for the additional details.

Wires
 

The received wisdom is that Mercedes allowed a subcontractor to choose stranded wire with a few large strands rather than many small strands. Such wire is less flexible and more likely to break. Add in 20+ years of work-hardening from the bending as the door opens and closes and you have a problem waiting to happen.

Jeremy

http://i323.photobucket.com/albums/n...ps69833cef.jpg

At least that is not the #1 bone headed subcontractor move of all time.

Dig into the real cause of Apollo 13 (the reports are on NASA's website) for that one.

http://history.nasa.gov/ap13rb/ap13index.htm

Jay bob pointed out this thread while helping out another forum member today:
http://www.peachparts.com/shopforum/diesel-discussion/319513-w124-electrical-fun-two-problems-4.html

It talks a lot about using connectors vs solder for fixing the wires between the door and the b-pillar. I hadn't found it in my own searches, so I have put the link here to possibly help out others in the future.

I ended up using crimp connectors, but like Jeremy, patched in longer pieces of new wire so the connectors were in the B pillar and door. I did have to stagger the connectors so they wouldn't all be in one giant bundle. I also used heat shrink. I'm not sure how the crimp connectors will stand up over time, but I was worried about my soldering skills in a cramped, dark space. I've had a little soldering practice between then and now so I may try soldering when I do it on the other rear door.

Thanks to Jeremy5848 post and others helpful comments, I've found one of the problems with my short circuiting rear window. To add a little, I was able to take the back off the male/pin side of the door window switch and remove the pins individually. I was then able to pass the whole assembly back thru door to get enough slack at the B pillar without cutting wires or snapping the plastic clips that holds the wires to the door. HTH.

Ended up with three broken wires at the hinge bellows.

Any input on soldering vs wire crimps?

Thanks!

Treetops

Impressive damage! Soldering provides a more durable connection but is more work than wire nuts or other connectors. Try to splice in new wires so that the connections ARE NOT in the rubber accordion.

Jeremy

I had this problem on my 85 300D.

I replaced the wires that pass through the B-Pillar with a 3-conductor flexible power cord with strong PVC cover - I cut a piece off a short extension cord. I added a separate ground wire taped to outside of cord. Then crimped to the car wiring at the floor, staggering the joins.

The mesh sheath that covers the wires on the original design, provides no protection. And it contains power wires and a ground. In my case the ground and one power wire were shorting out. I think that what happens, is that the opening and closing of the door tugs a bit on the wiring. The inside of the B-Pillar is not smooth. There are sharp edges on the inside of the door check and perhaps elsewhere too.

https://dl.dropboxusercontent.com/u/...en%20wires.jpg

That's good information, Graham. My '85 300D never had that problem but perhaps just due to luck (or repaired by PO). It may be that MB's sub switched to the cheaper wire in 1984-85, when MB was building the last of the 123s and starting on 124s.

Jeremy

I don't think it has much to do with the wire used . It doesn't break where it hinges, it breaks about half way down the B-Pillar on a straight run. Feeling up in there, there are some sharp edges. Either back of door check or just rough welds. Should have tried borescope to learn more.

It's actually a hard problem to diagnose, because it would blow the instrument lighting circuit, but only if the car lights are on AND the back door is opened! In my case, it also blew the traces on the cluster circuit board :( (covered in another thread)

80s Audis and VWs have this same type of fault. When I got my 5000 nothing worked - because most of the 30 or so wires going to the door were broken (the Audi had the window switches on the door as well as the seat memory and a radio speaker). They fixed this for the 99.5-2004 cars, however they forgot what they learned and the Mk5 cars have the same problem again. This is a bigger deal on those cars as there are airbag sensors inside the door.

-J

FWIW-i used braided 12 gauge wire, crimps and black tape. As Jeremy suggested I did my connections in the B Pillar and then again in the door.I tried to leave some slack in the B pillar to allow the wires to move during operation.

That done, now the pillar trim is on my dinning table paper clamped all over helping the glue dry...MBTex was in bad shape.

Probably in another thread somewhere, but how does one get the trim piece back on the B Pillar? (he clip at the top is a PITA...arggh)

Treetops

Trim reinstallation -- patience required!
 

There are some differences during the 10-year run of the W124 but from what I remember . . . after replacing the seat belt where it runs through the trim, you install the metal spring clip at the top of the trim and then pop it into the hole in the B-pillar. Then you try to get the seat belt adjustment slider to engage and hold while you put the bottom plastic piece on the trim, push the trim up against the B-pillar, and insert/tighten the two screws at the bottom. The most frustrating part for me is always the adjuster.

Jeremy