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Old 08-28-2004, 07:40 PM
MB FRAU's Avatar
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Join Date: Feb 2002
Location: Indianapolis
Posts: 39
How often does a wiring harness need to be replaced

Question: We had the wiring harness on our 93 400E replaced about 4 years ago. We are currently having some real issues with it. See following thread for more detail.

"Stumbling" issues with 93 400E

We were under the impression that once it was replaced that it wouldn't be an issue again. Is that true or is replacing the wiring harness something that will have to be done periodically even with the improved harness?


Joint Owner of:
'93 400E (80k miles)
- Smoke Silver/Parchment
'93 300CE Cabriolet (43K miles)
-Midnight Blue/Parchment
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Old 08-29-2004, 10:23 AM
Wes Bender's Avatar
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Join Date: Mar 2001
Location: Alpine, AZ / Green Valley, AZ
Posts: 733
I've never heard of replacing a wiring harness unless it was damaged to the extent that it was cheaper to replace than to fix. These are not replaced periodically as a part of routine maintenance.

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Old 08-29-2004, 10:35 AM
Glen's Avatar enthusiast
Join Date: Sep 2000
Location: Carlsbad, CA USA
Posts: 1,187
From personal observation and in talking with other owners, it appears the wiring harnesses in W124 models with I6 and V8 engines fail due to heat and age...but mostly heat. The insulation gets brittle and crumples away.

As I understand it, the replacement harnesses are identical to the original harnesses and will fail in the same manner. 4 years seems like a very short lifespan though unless your car and engine is subject to extreme heat all the time.
Glen Tokuhara
Beauty & the Beast and the wagon that could!
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Old 08-29-2004, 11:11 AM
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Join Date: Aug 2003
Location: Phoenix
Posts: 3,726
The replacement harnesses are vastly improved over the originals. The originals were made by a Swedish subcontractor with some ecological, biodegradable insulation that crumbles to dust in short order. I have never heard of a replacement harness failing and seriously doubt that wiring harness is your problem - unless it was somehow damaged. What is the clue that the wiring harness is the problem? Have you actually seen cracked or flaking insulation?
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Old 08-29-2004, 12:15 PM
Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
I agree the MB wiring harness problem is forever fixed with a new harness. The only problem is that there is not just one harness on the car. I have never had a chassis harness problem but v8s have an engine harness on the engine, an engine harness on the body, a battery,starter,alternator harness, and a harness that is part of the horribly expensive throttle motor assembly. All four of these fail during the years 93-95 when the insulation material was biodegradable.

It does seem strange that the rest of the car wasn't using the same insulation. Maybe it was, but won't show problems for more years due to the lack of the heat environment.

Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician
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