I started getting a message that my third brake light is out - but only intermittently, and like some other things, after the car sits in the sun. I've checked the connection, so I'm assuming the circuit board is just starting degrade. But before I spend $100+ on a new one, I figured I'd ask if anything else could cause it to fail just sometimes.

 

Mine did this, but all the LEDs were working just fine. So I removed it, and took the lens apart (you have to break it at the seam) to check for bad solders, etc. I tested all the LEDs and all was good. I put it back together with silicon sealant and all was well after that. I think the circuit board flexes and generates just enough electrical resistance that causes the error.

 

My wife (God love her) loves to slam the trunk closed. I've been through three third brake lights.

She is now banned from the rear of the vehicle. Hopefully my third light will me my last.

 

Yeah, slamming the trunk is not good, but I was always careful with my trunk lid and mine still broke. The C240 has never had an issue, yet the kid slams the trunk all the time - and it's been wrecked a few times. I think the CLK's has a design flaw. One think I did notice when working on mine is that the bracket and bolts are (as is usual) way over-engineered. I think the torque on the bolts is probably too high from the factory. It's just holding a piece of plastic in place - not securing a wheel or anything!

 

Yeah, I remember all the posts about people saying their third brake light just fell out, so when I saw mine I thought Hurricane Katrina could not remove that.

 

Yeah, mine fell out a couple of years ago. After replacing, no issues.

 

Had to replace mine when I bought the car, no issues since. Same with mirror turn signal.

 

I bought a replacement from ebay (from lithuania - $130 AUD delivered to Australia)

Just a minor problem. When I was tightening it up, the Red plastic popped off the grey backing. Oops.

Had to epoxy it back together, wait for it to dry, then reinstall, with gentle tightening....