CLK55_coupe_02

I have a bit of a weird question but I wouldn't be surprised if someone actually knows the answer.
The insulation over the wiring for one of the city lights (the H6 6W bulbs) cracked and peeled off so the wire touched a metal part inside the assembly. There are two wires, one brown and one gray. This was the gray one. It has a small cylinder on it that is shrink-wrapped in black plastic. Brown wire doesn't. This cylinder got extremely hot, the insulation melted off of it and it then melted a small part of the circular headlight assembly access door. This gave a bad bulb warning even though the bulb was still on. After a while it actually went off. I removed the circular small object, reconnected the two ends of the wire and all is well, bulb is on and no warning.

The question is what is this small object? It is about 3 mm in diameter, 6-7mm long and has small metal caps on both ends. The equivalent one on the other side has no markings on it, at least not on the black wrapping. This one is pretty charred. I am guessing it isn't a fuse, since it would have just gone out and it isn't easily replaceable. Is it some sort of capacitor? Do I need it? Where would I get one? Thanks in advance!

VIPclk320

is this a oem headlight or aftermarket? also if you post a picture i'm sure i can answer your question as i've messed around with the electrical system on the CLKs many many times.

CLK55_coupe_02

Thanks for the quick reply!

It is a stock headlight assembly. The actual city light bulbs I changed to LEDs (the ones with no error codes) but that was months ago with no issues.

Basically if you look at the city lights (the H6 6W small bulbs) the way you would if you were to change them, there are two wires going to them inside the assembly, one brown and one gray. The brown one is just plain but the gray one has a black section somewhere in the middle. This black section has a section in it's own middle that is about twice as thick as the normal wire (which is very thick for such a small bulb). This thick part of the black section is actually a small metallic cylinder but you can only see this once the black insulation burns away. Looks very similar to the type of things you see on circuit boards. It has metallic caps on both ends and a solid white surface in the middle. It is either a resistance, capacitor, relay or some other electronic thing like that. If that description isn't enough I will take a picture once I get home.
Thanks again for the help.

VIPclk320

if you are talking about the bulb itself then yes it is a resistor that allows the led bulbs to be error free, what that resistor does is pull in the same amount of current from that socket as a regular bulb does so you wont get an error message, the LED bulbs pull less current than the regular bulbs and thats why you need the resistors, some manufacurers started making the LED bulbs with the resistors attached to them and some sell it seperatly, and yes like you mentioned the resistor is normally attached to one leg only which is the posetive leg of the LED as the error message is trigered by the posetive on these cars. the only way to get a exact rsistor as the one that you have, you have to take it to a electronic shop or search online for "resistor measur reading" or "resistor color reading". on the resistor you will see some colored lines, ever line is in a different color which represents a different value once they are all added you get the total value(ohms) of the resistor and you can buy one the same value, and some of them just say the value on them in writting. its a very cheap item and can be purchased ant any elevtronic shop or online for about 10 cents. hope this helped and hopfully i was referring to the piece that you are asking about.

big_mike1979

I agree with Vip.. i got the led too.. i got the led and had to buy the resistor and the eq.

CLK55_coupe_02

I know what you guys are talking about and what those resistors look like, with the colored stripes on them but this isn't it. It does look pretty similar in shape. The LED assembly I got plugs straight into the H6 socket and whatever circuits and resistors it has are all incorporated in it, no wires, plug and play. The thing I am talking about is part of the car to start with, from the factory when it was running a halogen bulb. It is on the length of wire that goes inside the assembly from the wall of the assembly to the actual socket the bulb plugs in. I think the fact that I happen to be running LEDs has nothing to do with the whole thing which is why I didn't mention it at first. There was a short when the insulation fell off and the wire touched some metal and that caused this little cylinder to become very hot, melt some stuff and generally fail... I would guess it is a resistor that protects the bulbs since they are pretty small. The larger bulbs don't have it, only the running lights. I still wish I knew what it is but my guess is those LEDs will be ok on their own and the rest of the car shouldn't get damaged because this thing isn't there. Hopefully...

VIPclk320

to me it sounds like something maybe the previouse owner has added on there, maybe he or she was running regular LEDs and added that to not get the error. Again like i said earlier you would save yourself a lot of time and typing trying to explain it, if you would just take a picture of it and post it so we can actually see what you are talking about and maybe we can help.

CLK55_coupe_02

Camera battery was dead, will have it running in a little bit and post. But I don't know if it will show anything I haven't already described.

I am 100% sure this came with the car from the factory. The way it is connected to the wire, with some small metal collars and shrink wrapped could not be done by an owner, it is literally part of the wire... And when I bought it, the car was stock down to the very last bolt, even the battery, the tires, everything was factory spec. Seems like it was only serviced at Merc dealerships, not the kind of owner who rigs LED lights.

CLK55_coupe_02

Here are the pics. Penny is for scale. Like I said, a metal cylinder with metal caps that is attached to the wire at both ends. The black part is all there, all the rest was the gray wire, that is still on the car. The black insulation initially covered the cylinder. Any ideas as to what it can be?

VIPclk320

ok you got me on this one, I have never seen this before and i've messedaround with about 4 clk w208s. maybe someone can chime in.

CLK55_coupe_02

They are very easy to miss. Only the H6 city lights have them and only on one wire. And that cylinder thing is hidden under the insulation and only shows up as a slight thickening of the wire. To be honest I never noticed them until this one melted. But like I said I am almost positive they came with the car, the way they are attached is really flawless. There is no labeling at all, not even on the one that hasn't melted. Seems to be fine without it, at least for now...

unlukky

possibly a diode?

VIPclk320

you know what yu just nailed it, it is a diod, because the city lights come one when you lock the doors and leave and that means they get their power from the same source that turns on the dome lights inside, and they put that diod there so it would only be a one way transfer for the electricity. if they dont put it there everytime you turn on your city lights the dome lights would come on too, so i think the way its setup is that it takes the power from the dome light source to the city lights but blocks the power from going from the city light to the dome light. i just put a diod in my frineds 5 series because he wanted to have his halos come on when the doors where unlocked.

CLK55_coupe_02

That may be the case but I took this one out and the car behaves exactly the same, the dome lights and the city lights go on and off exactly like they used to. Also, when I lock the doors and leave, the fog lights and the position lights on the sides (yellow, on the front fenders) also come on, not just the city ones. I messed around with both (replaced the fogs with HIDs and the side position ones with clear lenses and bulbs) and I'm pretty sure neither of them has one of these diode thinghies... I think it is more likely it is some type of resistor to protect the bulbs from excess voltage, since they are small... Just a complete guess.

unlukky

If not a diode. Then it is probably a 'modern' fusible link. It will fail prior to sending voltage upstream to short the car out. < ? >

CLK55_coupe_02

It really does not look like a fuse type thing. It is inside the assembly, there is no way at all to change it if it burns. It is literally part of the wire, under the insulation and soldered to the two ends. Been running without it for a few months with no issues, hopefully nothing too bad will happen...

unlukky

Thats exactly right. It would be part of the wire itself. Old school cars had em on starters, ignition, etc. It went from regular wire to a thicker guage wire that was considered a fusible link. It'd burn prior to sending a catastrophe up or downstream. It wouldnt actually LOOK like a fuse. Not sure, just a guess.