Mercedes electrical issues


my 97’ mercedes c230 (100k miles) has a ghost in the machine…examples of issues include the winshield wipers when I turn on the left turn signal, random indicator lights (CEL, lamp out, etc) coming on and off at random and now the radio is turning off and then right back on again every few minutes. today, the car died on the highway with no warning or sputtering…just dead. it started right back up but still seems dangerous, doesnt it? any ideas?


Other than checking all the fuses, you are probably going to have someone do some troubleshooting of the electrical system. If you have a good independent shop it may be less expensive than a dealer.


any idea how much something like that will cost?


About $100/hour, times however many hours it takes. I would check the fuses and any accessible electrical connectors first.


Just a guess, but I would look into the main grounding wires for a problem. Possibly in the dash area also.

For the stutdown problem suspect the igniton switch, connections to it, or the main power buss near the battery. Make sure the battery connections are clean and snug.


I suggest you check the main grounding wires for a problem. Check the dash grounding also.

The shutdown problem may be due to a problem with the ignition power or switch. Check the main battery connections also and make sure they are clean and snug. You may be able find the trouble by tapping on suspected areas with a screwdriver handle.


Good point on the battery connections and ground straps, I don’t know how easy it is to get to the dash ground on that car.


This sounds like the classic symptoms of a degrading wiring harness. In the 90’s Mercedes used an ecologically friendly wiring harness that would break down once the car was in the bone yard. Unfortunately, the harnesses degraded many years too soon, while the vehicle had many years of life still to go. Mercedes wiring harnesses are not easy to check as most are wrapped in protective sheaths and covers. Carefully cut back part of an exposed sheath in the engine compartment and check for crumbling wire insulation. This insulation degrading allows for live shorts to occur and presents itself in all sorts of odd gremlins.
The dealer service manager or regional factory rep will know all about this issue and may offer some factory help on the repair. A wiring harness is not a wear item like brake rotors and such. The wiring harness should have a useful life of more than ten years. With any luck the dealer people will see it that way too.



I’ll second Benzman. While not a Benz guy, as an ex-SAAB tech I have seen this bio-degradeable wire harness problem on those cars also.

Even ran into this some years ago on a SAAB 900 I owned that was exhibiting some really stupid symptoms and every test showed the items affected were good, wire continuity good, etc.

All wire connectors and exposed wiring looked fine, BUT when I finally slit a wire harness sheath open with a razor blade almost all of the wiring in there had rotted, insulation wise.

It was easily spliced; the problem was figuring it out to begin with.


wow. thanks for that information…I’m going to call the benz dealer right now.


This is the first I have heard of such a thing as degrading insulation. While I can see the reason why, it really sounds like a bad idea to me. Unless of course you are the one selling the replacement parts.

I can imagine what a new wire harness for a Mercedes would be. By the time it was installed you could buy a nice slightly used Japanese car. Though maybe the enginners were counting on you to just scrap the whole vehicle after 10 years and buy a new one. This makes good business sense for the manufacturer to keep the production line going.

Thanks for the info Benzman.


Was the infamous wiring issue still going on in 97, I thought it was earlier? If that’s the case, I would just toss in a new harness.


List price for the harness will be around $740, with about 2 hours labor to install. If you manage to get some factory help, this might be cut in half. The car is ten years old and has 100k miles, so the factory may say the part “wore out”. Myself, I don’t care if it’s a Yugo or a Mercedes, the wiring harness should last longer than ten years. What the factory will not tell us is if the new harness is the exact same thing, or if it’s an improved version. Otherwise, plan on replacing the harness in another ten years…



I know a lot of owners are PO’d over this issue (because it really is a design defect, not just a matter of something wearing out), but we are really only talking about $100 per year, even if you have to replace it every 10 years. It’s really not any worse than my AC compressor that has a tendency to eat itself every 150K miles, or so (more like $200 per year, in my case).


hmmm. interesting. could you elaborate on the bizarre saab symptoms. i have a saab 900 that is exhibiting this out of the blue cut out behavior. saab techs cant make it act up and are recommending we replace the ignition switch. i wonder if they have checked this harness


What year SAAB 900 is it and any CEL illuminated?

There are a number of reasons why the car may cut out that are not related to a degrading wire harness.
An ignition switch is possible considering that many of them had the switch between the seats, where all the spilled soda and cookie crumbs gather!

In my particular case, the car would randomly not start or would run very rough while cold. Other times it would flood when hot. (caused by the cold start valve obtaining power at an inopportune time.)
The wire harness had degraded about 8" or so back inside the sheathing and the insulation on just about every wire was crumbling.

This harness had the wiring for the thermo time switch that controlled the cold start valve and also the wiring for the control pressure regulator and auxiliary air regulator. So yes, it created some real problems.

What are the details on your car? Does this car cut out at idle or high speed, stall at idle or low rpms, etc?
Does it do this in any weather; cold, hot, rainy, etc.?


An example.


this is a 98 saab 900 automoatic, and yes, the ignition is down low in the middle. bought last fall, this past spring it started cutting out with no warning whatsoever. sometimes at low speed coming to a stop, sometimes at mid range speed while accelerating, and i dont have the guts to take it on the highway. by cutting out i mean everything just blinks out and is gone. no radio, no dash lights, and most importantly no acceleration and no power steering. you just hope and pray you can coast to a safe stopping place. sometimes it will start right back up, other times it refuses for days at a time. the saab techs cant get it to act up for them and to my knowledge no diagnostic lights have come on for them. as for temperature, it should be noted im in phoenix and this all began when we really started baking around April. as im writing this the shop just called and they have gotten it to act up and are now telling me thye entire ECM needs to be replaced. they seem pretty confident this time, but this goes for 890$ new. thoughts? confidence in a used ECM? the car only blue books for 3-4K. thanks for any help