2002 E430, 161k

I was driving today and my 'defective bulb' indicator came on. Once home, I notice all lights were working. However, with the lights turned off, when I pressed the brake pedal, the passenger side low beam was coming on. Also, the 3rd brake light is constantly staying on and gets brighter when the pedal is pressed.

Does this sound like a brake light switch, or corroded connections? No sure where to begin looking.

Thanks for any help.

 

It sounds to me like a bad tail light ground connection. When the light circuit can not run easily to ground, it sometimes runs back through another circuit using it's ground. It causes some bizarre things to happen. In fact, when bizarre things happen, I always check for a bad ground.

The w210 has a known problem with the ground contact between the brake/tail light bulb holder and the metal of the tail light assembly. Start by removing the brake light bulb holder and look for discoloration on the tail light metal where the contacts from the bulb holder make contact.

 

OK, I just went and fiddled around out there. Here is what's happening:

With the car running and lights turned on, defective lamp message. 3rd brake light is lit without stepping on pedal. When the outboard passenger brake light assembly (plastic housing and bulb) are removed, the 3rd brake light goes off, and the passenger light low beam doesn't flash with the brake pedal.

I then moved this same housing and build and put it on the other side. Same thing happens, the 3rd brake light comes on and when I press the brake pedal, now the driver side low beam come (the bulb assembly is now on driver side). The suspect seems to be the bulb, which is doubtful, or the plastic housing that holds it. Do those housings go 'bad' or create issues like this? Anyone know the name or part number of the housing?

Any other ideas are welcome, I just don't like all of the brake lights on when I'm driving!

Thanks!

 

They do go bad. The circuit board that the bulb socket screws into fails due to heat from the bulb, plus excessive heat from weak connections over time. It happens in our cars and many others. Look at an older Jeep Grand Cherokee in front of you when they hit the brakes it's common to see strange things happening. A cure would be a new tail light housing

 

Hello, I'm new here and recently started to see the same issue on my E320. Bowyer, did you ever find out the root cause of this strange behavour? Thanks.

 

I replaced the bulbs and cleaned the area where the bulbs connect. It made the problem go away. Hopefully your 'fix' is as simple.

 

I had this problem off and on for the past couple of years. When it first started i did what folks above suggested..checked fuses, break light switch, bulb housings ...etc. To stay on the point...i was told by Master Merc. mechanic (right away when problem started)..to buy and replace both tail lights..i finally got tired of fiddling with it..both new lenses replaced them and problem went away.