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.

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