I'm very new to all this diy stuff, and my 3rd brake light isn't working. I've read that I need to take it to a MB specialist, but is there any way I can do it myself. The yellow 'error' light is driving me mad!!!!

Thanks
Lisa

 

Hi,
By 3rd brake light do you mean "high" brake light?

The error light is ON because one of your brake lights is OUT. OK.
There are 3 likely scenarios here.
1. If it is one of the regular low level brake lights that have gone you will need to replace the bulb. Straight forward. There is usually a hatch/cover to gain access to the bulb holder.
2. If it is the high lamp (which is usually LED subject to model) then either:
You need to replace the unit. You will need to order this part from MB. Access can be a little tricky often requiring the boot lid trim to be removed (Firtree or similar clips) or
3. The wiring to the high stop lamp has become disconnected in some way. You need to eliminate this possibility by ensuring power is reaching the unit when the lamp is supposed to be on.

All quite straightforward subject to your skill level.
Good luck.
Stuart.

 

Hi,

By 3rd brake light I mean the one on the boot. Everything was ok until the brake light on the drivers side stopped working, I replaced the bulb expecting the error light to go off but it didn't. When I checked again the light on the boot had stopped working. I read somewhere though that the error light on the dash isn't connected to the boot brake light though so should it still be illuminated??

I don't know if it's possible for me to have to dislodged a wire when replacing the bulb, but I'll take a 'novice' look at it and see if I can see anything.

Thanks for your help
Lisa

 

OK.

The 3rd boot light is an LED. It is unusual for these to totally fail.
I believe you are correct in stating that this is not monitored by the "bulb out" warning light since the unit has multiple "bulbs/LEDs.

Power reaches the main rear light clusters via a multiplug (something like 6 wires) from the PSE unit (RH side of boot below the floor)which does the controlling.

Access to change the RH brake bulb is thru a hatch on the RH boot liner which also gives access to the roof pump.
Did you just remove the brake bulb holder / bulb or the whole cluster? Does the RH brake light now work? Was the displaced blown when you tested it with a tester / eyesight? Are you sure it was the correct type of bulb. Single contact 21watt? I've seen people fit two contact (brake/side light 21w/5w) and side/tail light bulbs (5w). These might work (incorrect intensity) and give a bulb out warning.

Do ALL other external lights on the car work with the exception of the boot 3rd brake light?

Do you live in the USA? If so there is a recall (subject to VIN number etc) regarding intermittent brake light operation which may effect your vehicle if indeed the bulb you replaced was OK.

Only a couple of things I can think of that might be causing your problem.
1. There is a connection in the wiring harness that supplies the boot brake light (hidden behind boot lid panelling. How this could have become disconnected is however a mystery.

2. Does your Interior dome light work correctly? Do your doors lock/unlock correctly with the remote? Does your security system work correctly?
All these systems are controlled from the PSE and PSE's give problems which include false bulb warning.

However I struggle to find a link between replacing the RH brake bulb (warning light on) and subsequent failure (total) of the 3rd boot brake light.

Stuart