Hi, have a 2000 clk 430 cabriolet, 43,000 miles. I have these issues;
1. Reverse lights don't work
2. Third brake light inop
3. With no key in ignition if you open the trunk the dash lights flash and a buzzing and "motor like" sound comes from the right rear of car, in the battery area but back inside the trim somewhere. When you close the trunk, everything is normal.
4. Self dimming mirrors inop
5. Sometimes the right mirror doesn't return after reversing.

 

Took car to the dealer, the problem was two wires, one big ground and one other in the trunk lid harness. Had to be in pinned and pulled out to repair cut wires. Evidently a pretty common problem even in cars still under warranty. I guess they travel through a metal spiral sheath and there lies the problem.

 

The symptoms can be very perplexing.

In my case, it started with an occasional lamp out warning, upon braking, which could easily be dismissed by recycling the display using the steering wheel button. One day, after closing the trunk, the lamp out warning always triggered upon braking.

Found that none of the lamps located on the trunk lid to be working (backup, 3rd brake light, rear fog, license plate etc.). With the car turned off, opening the truck operated the passenger side mirror and then the electrical radiator cooling fan at full speed. If I opened trunk while the engine was running, the dash also lit up and flashed like a Xmas tree. Closing the trunk or holding in the trunk's courtesy plunger, stopped the ill effects.

At the time, I found the following thread, concerning broken wires within the trunk lid hinge wiring harness.

http://www.benzworld.org/forums/w208...t-problem.html

The reason for the strange interactions with other systems is that communication between the numerous vehicle control modules is via the CANBus. To save on cost and weight, voltage encoding is used. This allows the various voltage levels on a wire to create channels, where a single wire can control/operate several devices. To make a long story short, when a broken or short circuited wire (e.g. especially a ground return), occurs, the channels may no longer be totally isolated from one another.

Although the harness sleeve is rubber, I believe the harness length, between the trunk lid and quarter panel, is to short and/or it's mid anchoring point, causes added strain/flexing, resulting in broken wire(s).

I have also read where wires within the electrical harness for the soft top cover have broken as well.

Glad you got this squared away. Sounds like your dealer's tech knew what to do and the cost of repair was not to much.