Hey everybody,
I searched on this and couldn't find a solution, so I'm asking for some suggestions. The 3rd tail light abruptly quit working the other day on the e300, all other tail lights work fine. So, I have removed the cover, and checked the bulb (works fine.) I removed the housing from the rear package shelf by prying up on the little fragile plastic tab and there is no corrosion. (I cleaned it and applied bulb grease anyway.) I hooked up a multimeter and I'm getting zero volts between the contacts where the housing mounts. I checked the fuses to the right of the turn signal lever and all were good. Is there another fuse somewhere for the third tail light? Is there anything else to check? I did have a "bulb defective" display a few days ago, but I don't know if this is involved in that disasterous system, or if it could cause zero power to the 3rd brake light asembly. Any suggestions are appreciated- J

Power comes from fuse box that is part of the headlight switch & is also the lamp control module.

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

Thanks doc! So, how would I get at that headlight switch/lamp control module? I'm attaching a pic of the side of the dash where the fuse box and headligh switch are. All those fuses are good- so would I need to remove the lower panel to gain access? Thanks again for the help!

Attached Thumbnails

 

So, to update things somewhat, the third brake light is still not working. I researched a couple of other threads and have since checked for power at fuse #2 in the fuse panel pictured- with key on and pedal depressed and there is NO power getting to fuse #2. I don't know if this now points to the headlight switch as the culprit or if there is another fuse of relay in the circuit. Any ideas?

Um.. So could somebody please gimme a hand and share some advice or a wiring diagram with me on this? I have zero power to the #2 fuse and I don't know where the problem could be. I'd consider the brake switch, but the other brake lights are still working. I don't know if the headlight switch would be at fault if the other lights are still functioning. Anybody?..

If you jump 12V power (fused) to that fuse, does the lamp come on?

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

Hi Doc- I'll try jumping the fuse tonight and report back!

Hi Doc-
Well this has been interesting! I'm not entirely clear on how/why this had the outcome it did- but things appear to be in working order for now..?

After the post from Doc, I hooked up my multimeter and checked fuse #2 again and it showed nothing on either contact. So, like before, I removed the fuse, checked it over and put it back in the slot again. Then I fiddled around a bit- and checked it again and "pop" the fuse blew. I thought that was really weird. So I replaced the fuse with a new one- and now the tail light is working. I will keep an eye on it and see if things change but for right now it appears to be working, and it looks like it might have just been corrosion at the fuse (even though it had been removed and put back in the slot several times, etc.)

Just wanted to post to (hopefully) close this out. The 3rd brake light is still working since the fuse replacement a few days ago. I'll point out that the #2 fuse was removed and re-installed several times (always visually inspected not blown), and there was no obvious sign of corrosion on the blades of the fuse, nor any obvious indication there was a faulty connection at the fuse terminal. Checking continuity of the fuse with the fuse in place- showed the fuse was good. I was going to jumper the fuse with a fused 12 volts as doc suggested, after I checked continuity with the multimeter one last time. I was holding one probe on the fuse firmly, and when I dropped the other probe it grounded on my jack (under the car for another issue) which blew the fuse. I replaced the fuse- and the auxillary tail light is now working.

I honestly haven't had this happen before on any of our cars, (fuse not making connection in it's holder) and can only assume it has something to do with the quality of various electrical components we all know were used in the 90s and forward. I suspect the only "fix" would be a preventative meausure, and would be to remove each fuse, hit it with sand paper- slather it in dielectric grease and replace. Thanks to MBdoc for the help! -J