Well I finally took the brute force approach to solving the Light Malfunction Annunciator/Pest.
I was having limited success cleaning the contacts on the light bulbs, the holders and even the contact surface on the conductor plate.
I determined that it was the stoplights that were the main offender. I suspect the contacts couldn't take the current or had high resistance, so I decided to create some jumpers to augment the circuit.
I haven't had the Annunciator complain for 2 months now -- so I think I can claim some degree of success.
Here's how I did it.
I soldered pigtails onto the end of the contacts in the light socket -- butt soldered, not drilled through.
The blades are a spring steel and don't drill easily, but they are tinned so it's easy to make a solid and strong butt joint ( and there isn't much space for anything else.
I tinned a pigtail with a very short stripping, and then put a dab of solder on the point of the blade that lines up with the holes I drilled in the holder. You need the short stripping to avoid a long un-insulated "neck" on your finished project - to short out.
I recommend pushing them out one at a time. Maybe it's just me - but I found them amazingly easy to get mixed up. They push out easily by depressing the locking tab and pushing them up. Remove the bulb first though. It was just easier to photograph this way.
After soldering on the pigtail, I threaded it down through the matching hole. I used a #27 drill, but anything around 3/32 or so should work.
I crimped on the fasteners afterwards.
The first version just had spade terminals at the end of the pigtails, and I drilled small holes in the conductive plate and screwed the terminals to the plate with small tapping screws ( #6 x 1/2" ). This next version has spade connectors so I can pull the holder out of the car without tools. The pigtails are long enough to change bulbs, though if you want to keep the work simpler.
Notice the marks along the edge of the holder lining up with the contacts. I found this helped with determining the exact portion of the conductor plate that matched up with the specific contact. It can get mixed up and the resultant short will eat fuses.
I drilled the holes in the plate without removing the assembly from the car, so I "submerged" my drill bit in the drill so it was less than 1/4" above the chuck face. This was done so the drill didn't suddenly fly through the plate and make unwanted holes in, say, the tail light lens, for example.
Mercedes Benz should send you more than just a thank you note for your investigation and fix. So many owner are complaining about the problem. But what has MBZ done?
Damm, someone who pursues the issue. MB would have replaced the sockets!
Peter - The sad reality is that I had a spare set of sockets to play with because I went to our local dealer and spent $27 getting 2 new sockets and 2 new bulbs thinking this would put it to bed once and for all. I also took a Dremel tool and buffed the contact area on the conductor/plate.
As you can guess - to no avail[:(!]
I suspect the contacts are under-engineered for the amperage of the stop lights, and they go up in resistance, or change shape from the heat of the current and cause the error - just my guess - but it's obviously no worse than the pencil heads in Stuttgart.
This leaves the sockets as not much more than holders for the bulbs....
quick fix, at the dealer we replace the tailight assy, circuit board corroded or burnt up
sometimes its just the contacts on the socket that are bent or corroded, we'll just install a new socket
quick fix, at the dealer we replace the tailight assy, circuit board corroded or burnt up
sometimes its just the contacts on the socket that are bent or corroded, we'll just install a new socket
Replace the tailight assembly ? Is that a bit expensive and extreme?
Then again, maybe not -- I replaced sockets and bulbs with factory units and carefully buffed the contact points on the circuit board / back board -- to no avail.
That's why this unusual approach -- to avoid replacing the assembly to only face the trouble in a few years again.
This process only takes 45 minutes or so once you figure out where you are on this.
This assembly was under-engineered. This should never happen.
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