I'm about to tear this damn car apart.. I just replaced the 3rd brake light (only because of a couple dead LED's) back in November and last week the 3rd Brake light warning light came on.. i figured the new part just went bad.. Definitely not.. put the old one back in and still nothing.. checked the fuse and it's good. I have 2.5 volts at the hot side of the fuse, but only millivolts at the 3rd brake light connector. Tried following the wire as much as i could and didnt see any breaks in the wire. Tried to do a continuity check and the multimeter would beep like there was continuity, but it still showed overload.. wtf?

Does anybody have the schematics of the 3rd brake light? Is there a relay that it goes through?!? Everything else is working perfect, but this is about to drive me crazy..

 

https://mbworld.org/forums/3694210-post1.html

 

Haha I have no idea how I looked over that section. Got it fixed. Thanks a lot.. You saved my sanity.

 

I just had mine replaced at the dealer too. The gasket around the 3rd brake light was bad and letting water in..shorted the LEDs on side.

 

Excellent resource!