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3rd Brake light warning

20K views 41 replies 12 participants last post by  Corradoman12 
#1 ·
Hi everyone

when I initially test drove my 350, a warning message came up about the 3rd brake light, and indeed it was not working. We turned the ignition off and restarted and all was OK. The garage said they would investigate, but found nothing wrong. It has been fine for a few days, but came up again yesterday. I turned the ignition off, restarted, and all was OK. The car is under warranty so I am not too concerned, but just wondered if anyone has had the same issue or has an idea what the issue is?

As this is an intermittent fault, I'm also wondering where it is best to take it to a) Mercedes, b) A good Indy or c) Autoelectrian?

Thanks

Nick
 
#2 ·
#5 ·
Other brake lights (the ones at the rear/tail lamp cluster/assembly) are working?
 
#6 ·
Yes, the 2 outer brake lights work fine. Both times the error came up, the boot had just been opened, so maybe pointing towards the loom. At the weekend, I will give the cable a shake and see if the light goes out. Will post back the outcome.

cheers

Nick
 
#7 ·
I hope it is as easy as giving the loom a shake but it may well take more than that. You may need to figure out which wire is the one you suspect and get it separated from the rest of the loom enough to really move and bend it to make sure it does not have a break in it. Good luck.
 
#8 ·
i had the same issues (very intermittent ) for about a year
every time i took it to mercedes it would start working fine no problem with the loom. they said it could be the led unit but couldnt be sure and quoted me 250 quid to replace it. replaced it myself for £80 genuine mb part problem solved
steve
 
#9 ·
If it is the wiring loom, the rear license plate illuminating lamps may also be affected.
 
#10 ·
Well had a go at reproducing the fault at the weekend by moving the loom, no success. Next step contact the dealer and ask how he wants to proceed with fixing it. The dealer (non-franchised) is over 200 miles from my house, so I need to arrange for repairs, get his approval and then send him the invoice. Will let you know the outcome.
 
#12 ·
The light unit was replaced and all seems well now. However, I successfully ejected a CD from the 6 CD changer and now I get drive unavailable message. I'm hoping it is because the car was really cold and perhaps the mechanism is stiff. I can hear the CD changer making noises. Will have to investigate further.
 
#13 ·
reset battery if you haven't

disconnect neg cable for a minimum of 30 minutes
reconnect
resynch window n reset clock
try cd
 
#19 ·
A wiring loom is a group of wires. The loom referred to here is the group of wires that goes from the trunk (boot) up the left hinge to the electrical components that are connected to the trunk lid. As the lid is opened and closed many times the bending of the wires in the same spot over and over can cause one or more wires to actually break. With the brakes lights on (have someone sit in the car applying the brakes or wedge a board between the seat and brake pedal) take a hold of the loom and move it around as it would with the lid closed and opened. If the brake light in the lid goes off then you have found your problem.

At that point I would have the seller do a proper repair of any damaged wires in that loom (all are suspect).

Good luck and let us know how it turns out.
 
#23 ·
My auto-electrician removed the 3rd brake light and connected to a power source. It seemed to work fine, so he tapped it a few times and all seemed well. He then twisted the unit slightly and the lights went out. He was able to repeat this several times proving the light unit to be faulty. A new unit from Mercedes, approx £50, solved the issue.
 
#25 ·
I've just gone out to the car but noticed as I started to drive off that I had no front lights on and the third brake light warning was on again. The lights will come on if I manually put them on and they come on when I unlock the car with the fob, so the lights themselves are working, I'm guessing it must be that loom thingy.
 
#29 ·
Remove the negative cable from the battery
wait 30 minutes
reconnect neg cable
reset clock
resynch windows
 
#33 ·
I've gone to give it a go this morning but unfortunately failed the first intelligence test as I don't know how to open the bonnet :|

I'll take it to the garage next week, probably best.

Thanks for your input guys, I'll take a print out with me to my garage.
 
#37 ·
I have this problem here and there, and it is usually when the battery is low on voltage and i also get the esp warning come up to, once the car is taken for a run (not used often enough) it is fine and no issues for a while, these cars are massively battery sensitive and like to throw a wobbler if not fully charged.
 
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