3rd Brake light warning

Check the trunk wiring loom. That is usually the fault
it is the loom that you see when the trunk is open.

https://www.google.com/webhp?source...ld.com r171 trunk wiring loom 3rd brake light

Thanks Jeff, I'll take a look at the loom.

Cheers

Nick

A session with the car connected to the MB DAS system (diagnostic system) could tell you exactly where to look for the problem.

Other brake lights (the ones at the rear/tail lamp cluster/assembly) are working?

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

Nick D said:

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

Click to expand...

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.

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

If it is the wiring loom, the rear license plate illuminating lamps may also be affected.

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.

I had an auto electrician visit yesterday, after a lot of wriggling the loom and then removing the light unit, finally determined the light unit to be faulty. Replacement being fitted on Tuesday. Will update on the outcome.

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.

reset battery if you haven't

disconnect neg cable for a minimum of 30 minutes
reconnect
resynch window n reset clock
try cd

Looks like I have the same problem. Initially intermittent, but now persistent third brake light error. Any idea about cost if the loom is faulty?

Would be a lot easier/cheaper to just open it up and replace the broken wire(s)...

I too have this as an intermittent fault. My local garage checked it over and said everything is working. It will disappear for weeks at a time then suddenly reappear. I've no idea what a loom is :frown:

A loom is a collection of electrical wires.

When you open the boot have a look underneath the lid.
Is it wet?

Damp can 'irritate' the electrics.
You get a fault, go the garage, presto....no fault.

DeeJ said:

I too have this as an intermittent fault. My local garage checked it over and said everything is working. It will disappear for weeks at a time then suddenly reappear. I've no idea what a loom is :frown:

Click to expand...

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.

Thanks, guys, useful info. It's gone again at the moment, came on the other day for 10 mins then disappeared. I'll keep an eye on it.