I recently Engine Degreased my 82 300d Turbo at a self service carwash because it was disgusting. An odd, thing I noticed after I left the carwash was that the left Headlight stopped working. The right one was working fine however.

I pulled off the headlight cover and unplugged the headlight connection from the housing of the headlight and checked the voltage. 11.84 volts. It has juice. Maybe the wiring inside the headlight housing is bad? I checked those wires right on the connectors of the headlight. 11.84 volts. Even though I tested the ohm rating on the bulb and it was a continuous circuit, I said what the hell and bought a new blub. However, the new bulb will not work?! I blew out the connectors with compressed air and even slightly crimped the three connectors with needle nose pliers a bit so that they will make better contact, but still no light.

What gives eh?

If the high beam is also inop. you've lost ground. 1 wire, low beam, other wire high beam, 3rd wire ground at the head light plug. I presume you have Euro lights?

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81 300CD (sold) 1972 280 SEL 4.5 (sold) 1966 250 S 4 spd (sold) 1974 450 SL (sold) 86 BMW 325ES (sold), 1973 280C (sold) 1988 300 SE.

There must be more to this story.

If you've got 12V and a ground, the bulb must light.

When you checked for voltage, did you use the ground on the plug........or did you go to the battery or the engine for a ground?

I am unfamiliar with the difference between euro and noneuro lights. They are the round kind. That is all I can really tell.

I used the ground from the plug. that is what is strange. I thought perhaps maybe I was gaining resistance somewhere, and maybe since it was a halogen bulb, maybe I wasn't hitting some critical voltage.

To answer a previous question, the high beams are inop as well. But that would only make sense because high beam and low beams are just both terminals on the bulb. If there was a problem in the wire, both wouldn't work.

If the voltage at the plug is 11.84..........what's the battery voltage?

Measure the resistance to ground on the ground socket in the plug. You should get 0 ohms (continuity).

High beam, separate filiment inside the lamp. Again if both hi and low are inop and both their plugs have voltage, then you have a lack of ground. Strip back a little insulation on the ground wire close to the lamp and run a new wire to a shiney metal ground underhood. If the lamp now works look for loose, corroded ground circuit to that bulb.

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81 300CD (sold) 1972 280 SEL 4.5 (sold) 1966 250 S 4 spd (sold) 1974 450 SL (sold) 86 BMW 325ES (sold), 1973 280C (sold) 1988 300 SE.

Battery Voltage is 12.3 volts.

Okay, I will test out these tomorrow and see what happens. I'll keep you guys updated. Thanks for the help. You guys are awesome.

I think you got it in one. The resistance of the DVM is so high that a small resistance in the ground wouldn't affect the voltage you read by very much. However, it won't take much resistance to make the headlights not work.

The resistance in the ground and the resistance in the DVM create a voltage divider, so the DVM reads only a percentage. For example, if the DVS is 1 million Ohms, and the ground is 50 Ohms, the DVM will see 99.995% of the full voltage. The lights, however, are probably closer to 2 Ohms, so will only see 3.8% of the applied voltage (or about .5V, not enough for them to even get warm). If you slide the pins out of the plug enough to measure the voltage across the bulb when it is in the circuit, you'll see the lower voltage I speak of.

I've gone into length on this because with only 12V to work with, almost everything has a low resistance. The voltage divider effect is something to be aware of when measuring with a high resistance DVM. Of course, if you always measure acorss the load itself things will become a lot more obvious.

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'83 300DTurbo http://badges.fuelly.com/images/smallsig-us/318559.png

Broadband: more lies faster.

Update time. Okay, I stripped a bit of wire right in front of the ground and it works! I changed out the right light housing with the left one, and CURSE OF ALL CURSES it works! Why is that bad? Because now I know the problem with the ground is not in that really short wire between the car and the light.

I was wondering something. What if I took the cheap way out and just pulled a wire from the light housing wire after the connection to the car, to a piece of metal on the car for grounding. Would that mess any other system up, or would it actually work?

Should work. Make sure new ground wire is soldered to the existing wire and other end to a shiney clean surface. Did you ever check the fuses? Mercedes uses a fuse for each headlight. Pull the correct fuse and replace it no matter what it looks like. they sometimes corrode and appear fine.

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81 300CD (sold) 1972 280 SEL 4.5 (sold) 1966 250 S 4 spd (sold) 1974 450 SL (sold) 86 BMW 325ES (sold), 1973 280C (sold) 1988 300 SE.

Well, pardon my ignorance, but is the fuse on the ground wire on the way back to the negative terminal? Wouldn't that make no sense? If there was some sort of short close to the light before the fuse on the ground wire, wouldn't that blow the bulb and pull monster current?

Also, the foglights work like a charm and If I am not mistaken, they both use the same ground wire. Why do the fogs work and not the headlights?