Lessons learned: W124 B-pillar wiring problems - PeachParts Mercedes-Benz Forum

Jeremy5848 · #1 01-18-2009, 10:11 PM

In April 2008 I posted a thread here about repairing broken wires in the B-pillar of a W124 car. Even though I was able to fix the power window problem, I could not get all of the puddle lights to work (in the bottom of the doors, Mercedes calls them "exit lamps"). The driver's door was especially troublesome – it worked but was very dim. [Wasn't the bulb or socket – read on.]

This weekend, after agonizing over the schematics and tearing open both the LF and LR doors and the left B-pillar, I finally traced the problem to a broken wire in the left B-pillar. [See the first thumbnail photo.] One of the hot wires (red w/yellow stripe) feeding the puddle lights had broken in half. The plastic tubing also was badly broken. Interestingly, the other three wires were undamaged. I repaired the wire and the puddle lights returned to normal. Took half of Friday and most of today, 85% to find the problem, 5% to fix it, 10% to put the car back together.

Learnings from this project:

1. B-pillar wiring is definitely a nemesis for W124 owners.

2. The wiring of the puddle lamps is not exactly as the FSM shows it. Well, it is called a schematic diagram so I should have been more cautious – a schematic is not supposed to represent exactly how the wires are routed in the car, although they usually do. Not this time. The driver's door seems to be last on the list, not the first. Oh well.

The yellow coloring in the following diagram shows that the LF puddle lamp should get its power from fuse "C" and connector X18 (located under the fusebox). It does not. The LF puddle lamp gets its power from the rear of the car via the LR puddle lamp. Perhaps the wires circle the car starting on the passenger side. Caveat emptor!

3. Removing the door skins has never been a problem for me but re-installation is another matter. I found the following steps worked for me. YMMV.
(a) It helps to know where the various plastic hooks are that hold the skin to the sheet metal. Mark the position of the hooks with tape on the visible side of the door skins. [See the second and third thumbnails. The red stars were added in Photoshop.]
(b) The rubber seal strip at the lower inside edge of the window is best attached to the metal frame of the door. At least I had better luck that way than by putting the strip on the door skin and trying not to have it fall off in the middle of the job.
(c) Hold the door skin up to the door and then thread the manual lock knob through the hole and onto its threaded rod. You can't get the rod through the hole once the skin is on – the clearance is too tight.
(d) Make sure the wires for the puddle light and power window are through the correct holes. They're hard to get at once the skin is on!
(e) It seemed to me that the hooks in the middle of the door skin were a little longer than the others so I hooked them first, then the hooks around the outside edges. You may find that it helps to have a few extra hands to help in pushing the door skin tightly against the door as the hooks are engaged.
(f) Now hook the upper part of the skin over the edge of the door and onto the metal clips. Use a soft mallet to gently but firmly tap the skin down to securely engage all the hooks.
(g) Re-install all of the door hardware and you're done.

Jeremy

sixto · #2 01-19-2009, 01:04 AM

Jeremy, my car had a similar gap between the front door pocket and armrest because of a couple of broken clips. I used some long screws to affix the pocket to the armrest from the hidden side of the door liner and it looks a lot better now. Alternatives are obtaining a good used liner or buying a new one.

Sixto
87 300D

Jeremy5848 · #3 01-19-2009, 01:08 AM

Good idea, Sixto. Mine actually looked even worse before I added a little Gorilla Glue. I'll look into some screws next time it's off.

Oreo · #4 05-03-2009, 01:36 AM

Hi Jeremy

I'm glad you put this info up. I have a problem now with just one side of the car's exit lights. I traced all the wires from the fuse box to the kick panel to the faulty side B pillar. I think my problem could be in the opposite side B pillar now if the supply is coming from one wire going around the car. My wiring diagram shows 2 wires split from the junction box in the kick panel and then they disappear into the bowels of the bodywork.

My guess is that the weak point was in the flexing at the door joint but was stumped when I found no power supply from the faulty side B pillar. So the break has to come further up the circuit and the only other point could be the opposite B pillar. Can't be the A pillar since the 2 doors of the good side are working.

Andrew