Broken window wires in W124 B pillar -- an example - PeachParts Mercedes-Benz Forum

Jeremy5848 · #1 04-10-2008, 08:16 PM

There have been many mentions of broken wires in power window threads here and elsewhere, especially involving W124 cars. The wiring that goes through the B pillar to the rear doors seems especially liable to fail. I thought you might like to see an example.

I had noticed for some time that the right rear window in my 1987 300D would not work occasionally. Then it changed to blowing the fuse (it's the "G" fuse in that car). Since the same fuse powers the driver's window, it was definitely worth fixing.

After removing the door skin and the B pillar trim panel, I removed the plastic plug body from the power window cable and pulled the cable out through the rubber pass-through. As soon as the cable came into view I could see the problem (first picture). I had expected the wires to have broken inside the cable and touched each other; what I saw was that the wires had broken through the cable, allowing the raw ends to touch the body of the car, causing the fuse to blow when the window was operated. It looked like the cable had been tied in a knot! (In defense of Mercedes, this might have happened when the PO installed his aftermarket alarm system.)

With the cable sheath cut away, the damaged wires -- two were actually broken -- could be seen. The overall effect was much worse than I had expected. No wonder it blew fuses!

After repairing the breaks and properly insulating the wires, I put everything back together. The window now operates correctly and the fuse doesn't blow. Makes you wonder what the cables in the other three doors look like!

Jeremy

babymog · #2 04-10-2008, 08:29 PM

Looks so uniform, like it was cut or pinched. Is the insulation brittle or pliable?

Jeremy5848 · #3 04-11-2008, 12:01 AM

It's possible that the wires got caught in the door edge and pinched, even though the rubber is supposed to protect it. I was really surprised to see how twisted and knotted the wires were. It's hard to imagine how that could have happened.

The insulation is not brittle but far from new -- the car is 20 years old, after all. Given that, I suppose most of us should replace all of the door wires in all of our "old cars."

Chad300tdt · #4 04-11-2008, 12:16 AM

I had to strip new wires in for the passenger side rear door in my wagon too. When I pulled the outer sheathing off, the wires looked shattered inside. It's nice to have all the windows working.

MBeige · #5 04-11-2008, 12:20 AM

On the W123 at least, if you look at the B pillar there's a plastic cover at the base. Remove it and you'll see the vacuum lines and wires leading up to the rear doors. There's a bracket that holds them tight, it might be possible to release the slack at the hinge itself if you pull up on these. Then again that may also stress some of the wires and lines on the floorboards. If it applies to the W124 then I hope it helps

oso · #6 04-11-2008, 12:22 AM

So how exactly do you get the B pilar panel off? I have the rear door panel removed but do not know how to get to the wire.

Jeremy5848 · #7 04-11-2008, 01:34 AM

Quote:

Originally Posted by oso

So how exactly do you get the B pilar panel off? I have the rear door panel removed but do not know how to get to the wire.

Bear,

At the base of the trim panel covering the B pillar (the seat belt comes out of this cover) is a plastic panel held on by two recessed Phillips screws. Remove the two screws and then pull out at the base of the cover. It will come off.

Set this small panel aside (don't lose the screws!). Now you can pull the long cover off of the B pillar. It is held in place with a metal spring clip at the top. It is a little hard to pull off but will pop out if you continue to pull straight out. Once the cover is loose from the pillar, it is still held by the seat belt going through it. Rather than taking the seatbelt all apart, I simply stretched it out to the end of the roll-up mechanism and wedged the cover against the seat so it is out of the way.

Once the cover is off, you can look into the B pillar. Inside is the roll-up mechanism for the seat belt, including a tensioning device that is actuated by the airbag sensor, and the wires and vacuum hose that goes through the pillar and into the door. Some of the wires are attached to the door switch. The rear door switches (left and right) operate the "courtesy lamps" (puddle lamps) in the bottom of the doors and also the rear dome light. [In my car, each switch (left and right) operates both puddle lamps at once. I think it is supposed to do that but can't be 100% sure because the PO boogered the wiring.]

While the panel is off of the B pillar, look at the seat belt height adjuster. See how the plastic piece (trapped in the cover) presses on the spring so that the adjuster can go up and down. Understanding how this thing works will be handy when it comes time to put it all back together.

Putting the trim panel back onto the B pillar takes a little maneuvering but is not too bad a job. Position the spring clip at the top over its hole and smack it into place with a fist. Next, make sure the seat belt height adjuster is in the right place. Then press the panel against the pillar and work the edges into place alongside the trim strips on each side. You may have to use fingernails or a dull putty knife to help the trim panel fit back into its place -- it keeps wanting to pull the trim strips in with it. Once the trim panel is mostly back in place, put the lower panel back, press in and lift up, and put the two screws back.

Jeremy

oso · #8 04-21-2008, 11:32 AM

Thanks to Jeremy, now I know how to get to the "inards" of the B pillar and wanted to take care of another nuisance: slacked seatbelt. After it's unbuckled, the belt does not want to snap back, just kind of hangs there...What do I need to do to fix it? The cover panel is off and I am ready!

babymog · #9 04-21-2008, 01:46 PM

"lazy retractor". Germans are famous for them.

I suppose you could open it and put another turn or two on the spring, but I'm not sure it will open, not designed to be servicable. Also, be VERY CAREFUL with those retractors, they have an explosive charge in them to pre-tension the belt in a collision.

Personally, I have spares, but I'm not willing to open one and attempt service. Find one in a 300E in the boneyard that hasn't had airbag deployment and replace yours.

oso · #10 04-21-2008, 03:49 PM

OK so I was not blind not seing any easy way to jack up the spring induced tension on that thing! Will do as advised - thank you.

pawoSD · #11 04-21-2008, 07:05 PM

My seatbelt retractor is lazy too....all of them are. Mine is an '82 though....so I don't think it has the explosive pre-tensioner....

Johnhef · #12 04-21-2008, 07:19 PM

I just posted something similar to this, although in tech help a week or so ago

1986 300E window fuse keeps blowing

The wiring "knot" appearance is common, although you may only feel a bump under the sheilding, mine wasn't broken though on the outside yet.

Jeremy5848 · #13 04-21-2008, 07:51 PM

Quote:

Originally Posted by Johnhef

...The wiring "knot" appearance is common, although you may only feel a bump under the sheilding, mine wasn't broken though on the outside yet.

Interesting. I was surprised that mine was as badly damaged as it turned out to be. Wonder what the left side looks like... [I plan to leave well enough alone as long as it works]

Shortsguy1 · #14 07-20-2013, 05:44 PM

Quote:

Originally Posted by Jeremy5848

After repairing the breaks and properly insulating the wires, I put everything back together.

Jeremy (or anyone else who has done this fix)-
Could you provide more details about the actual wire repair. Did you solder in new wires, or use connectors? What actual length of new wire was needed? I assume stranded wire is better than solid wire, but is there a specific gauge and insulation type that I am looking for? How did you insulate the repaired wire bundle? I have no idea if heat shrink tubing will stand up to repeated bending like that. If I tackle this, I would rather not have to do it more than once (per door).

Thanks!

sixto · #15 07-20-2013, 06:25 PM

I was with Jeremy at a PnP and we (he did all the actual work, I cheered him on) relieved a '94 W124 of its left rear door wiring - everything in the door, down the B-pillar and to a convenient point in the wire channel by the driver door sill. The intention is to splice this 7 year newer wire at a point along the B-pillar or door sill away from the hinge. Effecting the repair in the hinge area seems like more work and doesn't address the rest of the original wires.

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Sixto
87 300D