C-Class (W203) 2001-2007, C160, C180, C200, C220, C230, C240, C270, C280, C300, C320, C230K, C350, Coupe

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Old 04-07-2009 | 11:11 AM
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Question Pop Quiz! Prizes offered...

What does this black ground wire go to? It disappears into a wiring harness between the fender and the battery, back by the firewall.

The MB roadside assistance tech who responded to a recent non-start situation could not tell me where this wire goes... only that it's a grounding wire (I could have guessed that myself, LOL).

When my new battery was installed two years ago, it apparently was allowed to sit on this wire by mistake, so the wire is now frayed back by the battery. I've wrapped it with electrical tape for now to keep it from shorting anywhere.

Any help appreciated.

Just teasing about the prizes...
Attached Thumbnails Pop Quiz!  Prizes offered...-ground-wire.jpg  
Old 04-07-2009 | 01:30 PM
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Originally Posted by MB-BOB
What does this black ground wire go to? It disappears into a wiring harness between the fender and the battery, back by the firewall.

The MB roadside assistance tech who responded to a recent non-start situation could not tell me where this wire goes... only that it's a grounding wire (I could have guessed that myself, LOL).

When my new battery was installed two years ago, it apparently was allowed to sit on this wire by mistake, so the wire is now frayed back by the battery. I've wrapped it with electrical tape for now to keep it from shorting anywhere.

Any help appreciated.

Just teasing about the prizes...
Disconnect and see what won't work properly afterwards.

Just teasing about that as well.
Old 04-07-2009 | 07:03 PM
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You are a big help!
Old 04-07-2009 | 07:07 PM
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I think that wire was added as part of the turn signal light TSB. It gets spliced into another wire that leads to a connector.
Old 04-07-2009 | 11:13 PM
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Something ist nicht charakteristisch und nicht richtig!

German cars usually use brown wires to connect to ground. Called circuit 31 on many drawings. Mercedes allows repairs of wiring issues, and thinks one should use yellow wire for repairs. This makes it easier for future tech's to see where there has been work done. This makes me think an outsider worked on the car.

One of my minions had a problem with their SL discharging the battery. Under the hood I found a similar wire. It was not on the car wiring diagram. It also disappeared into a harness. Chasing it down with a borescope, I found a 8x6x1 inch brick wedged between the inner wheel liner and the sheet metal inside the engine compartment. I pulled the brick out and had a look at it on the bench. The battery drain stopped when I took this box out.

Inside was a long dead (it was a MY 1995 car) gel battery. It said Kenwood on the label, but inside was a radio receiver and transmitter. It was a LoJack unit. The current driver bought the car 2nd hand and had no idea that there was a LoJack, so when the internal battery quit, it drew current from the car battery.

Is it possible you have such a device?
Old 04-08-2009 | 07:40 AM
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98 Black C43 , 08' ML320 CDI ,11 E63
Originally Posted by Moviela
Something ist nicht charakteristisch und nicht richtig!

German cars usually use brown wires to connect to ground. Called circuit 31 on many drawings. Mercedes allows repairs of wiring issues, and thinks one should use yellow wire for repairs. This makes it easier for future tech's to see where there has been work done. This makes me think an outsider worked on the car.

One of my minions had a problem with their SL discharging the battery. Under the hood I found a similar wire. It was not on the car wiring diagram. It also disappeared into a harness. Chasing it down with a borescope, I found a 8x6x1 inch brick wedged between the inner wheel liner and the sheet metal inside the engine compartment. I pulled the brick out and had a look at it on the bench. The battery drain stopped when I took this box out.

Inside was a long dead (it was a MY 1995 car) gel battery. It said Kenwood on the label, but inside was a radio receiver and transmitter. It was a LoJack unit. The current driver bought the car 2nd hand and had no idea that there was a LoJack, so when the internal battery quit, it drew current from the car battery.

Is it possible you have such a device?
Damn , thats some serious troubleshooting work !
Old 04-08-2009 | 07:52 AM
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Gents, the service tech said this was a ground wire, but of course we know how competent some of them are...

BTW, this wire does NOT appear to be any modification. It weaves seamlessly into a factory installed harness, and appears to be just as old as the rest of the wiring. Nor has my service dealer had the car long enough or for any past service reason to justify such a modification.

So, I think it's an OEM wire.

Some other guesses, please.
Old 04-08-2009 | 08:02 AM
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pick up
I wonder what is the prize?...lol
Old 04-08-2009 | 02:18 PM
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No prizes?
The service DVD has a bunch of wiring diagrams...
Old 04-08-2009 | 04:23 PM
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03 W203, 13 E350, 13 W204, 14 C218
I had the same problem! The dealer told me it went (oh wait...there are no prizes?) Nevermind.

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