While exploring the darkest areas of my '86 300E recently, I discovered that part of the wiring harness had a split-open rubber sheath and one of the wires inside had insulation missing ( I could see the copper!). The location is just under the brake master cylinder at the end where the brake lines are connected.

There are several branches of the harness at that point. The damaged section was the part of the harness which laid flat on the metal surface. About 6 inches of the harness was split open and a purple with yellow stripe wire had lost the TOP half of its insulation, not the bottom half. I slit the harness jacket back about an inch at each end of the damage. That purple wire was in good condition there. No other wires in the harness were affected although a heavy red wire's insulation looked a bit rough.

My theory is that some brake fluid had done the damage. I've heard that this fluid can damage paint but I've not heard that it could affect the wiring. Does anyone else know about this? I've not read of any general wiring harness problems with this year and model MBZ.

My fix of the problem was to coat the bare wire with about 5 coats of "Brush-On Electrical Tape" made by Blue Magic, Inc. I found this at a home improvement store's electrical department. I first tried it on a sample bare wire and found that it is very tough and sticks well after it dries. After coating the wire, I double wrapped it with 3-M Super 33 electrical tape, slipped on a rubber insulation jacket which I removed from a larger cable, and then enclosed the entire damaged section of the harness with a plastic split loom from an auto store. I never wanted to see any more wiring damage there!

The job wasn't to hard to do. I had to remove the vacuum line to the brake booster for clearance. There was only room for one hand, my right hand, so I did the whole job one-handed. I'm left handed so it was a bit awkward but not too bad.

__________________
1986 300E
1993 Volvo 940 Wagon
1984 Volvo 240 (daughter's)
1976 Dodge 1/2T pickup, gas hog

Great to know about "Brush-On Electrical Tape". I guess if the brake fluid corrosive enough to damage the paint then it is also harmful to plastic or rubber.

__________________
1996 E320 since 1/16/08, 171K miles as of Feb 2011

---------------------------------------------------------
1989 300CE - R.I.P. Dec 29 2007
Other MBs (sold): 1992 300E-24 - 1979 350SLC - 1984 230E - 1990 300CE

Hi,
Brake fluid should not damage the rubber.

__________________
2004 ML350 Black with charcoal leather, OEM Hitch, Rhino step, Bose, Navigation, OEM front guard, Comfort package, Entertainment package, Sunroof, heated seats.

I didn't think so either but something damaged that section of the harness. There is no heat source close by nor is there anything rubbing on the harness.

The rubber or vinyl jacket was split wide open. Only one of the wires in the harness was damaged and that one lost the insulation evenly on the top half of the wire.

The deteriorating harness I've seen had intact sheathing on the harness and the insulation on most wires was hard and brittle and would break off on chunks. My harness problem was very different.

'Tis a mystery!

__________________
1986 300E
1993 Volvo 940 Wagon
1984 Volvo 240 (daughter's)
1976 Dodge 1/2T pickup, gas hog