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Old 09-30-2003, 01:46 AM
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Merc Electrical problems??

My 1996 C class Mercedes has a number of unusual random problems which I assume are electrical issues and my mechanic has never seen it before.

Problem 1.
Basically on purely randon occassions the fan will come on full and cannot be turned off.

Problem 2.
The other random problem is all the following things all occur at once, the speedo stops, crusie control won't work and the 3 brake warning lights in the instrument cluster come on all at once and then the car won't idle properly. Then after doing this for a random amount of time everything goes back to normal and the car runs perfectly.

Both these problems occur purely randomly and of course did not occur in front of the mechanic. My mechanic could not find any problems.

I assume I have electrical or computer problems? Does this car have any inbuilt computers???
Help comments or help would be appreciated??

Last edited by Chambo; 09-30-2003 at 01:53 AM.
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Old 09-30-2003, 02:38 AM
Registered User
Join Date: Jan 2003
Location: USA
Posts: 699
Your 1996 C-class MB must have a bad wiring harness, in which the wires may get into contact with each other from time to time, causing unexplainable electrical problems. You have to replace it with a better wiring harness.

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Old 09-30-2003, 04:32 AM
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Join Date: Apr 2002
Location: Melbourne, Australia
Posts: 280
Unhappy wiring harness?

Hope I'm not going to have this in my 1994 C180! The wires near the engine block look like they have insulation material hardening and cracking up. I have tried to recover the wires with some tape material and also block the nearest metal surface with a non-metallic shield so the wires won't touch it and get worse. In the meantime, all goes well! What would it cost(total) to change the engine harness??? Can the indie do it correctly or only a dealer can???
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Old 10-06-2003, 12:22 AM
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I am now having an additional electrical problem , the red and green door lock/unlock lights will start flashing at unusual times such as when driving along.

Therefore my car now has 3 problems
1. Fan / heating turn themselves on randomly;
2. Speedo stops and dashboard brake warning lights come on randomly;
3. Door lock/unlock lights both flash randomly.

Can anyone have any suggestions as to what might be wrong??

Please help.
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Old 10-06-2003, 04:42 AM
Registered User
Join Date: Apr 2002
Location: Melbourne, Australia
Posts: 280
Unhappy electrical problems

You really look like you have the electrical gremlins that Mercedes has become famous for!!!! This seems to be pointing at harness problems and maybe replacement is likely to be the only solution.
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Old 10-06-2003, 07:51 AM
Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
Except for certain 92-95 modells, MBs never have wiring problems.

Except for those years, problems are almost always the connectors or the components themselves.

The answer to electrical problems with numerous symptoms usually means similar grounding points or similar power sources. The only way to deal with this other than when its happening is to look to the wiring diagrams and identify the systems involved and their power and ground similarities.
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician
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