Now you see it, now you dont...headlight woes

[iceman3876]

1993 300D 2.5l right headlight has a problem. I have hesitated posting a thread before exhausting possible solutions to a headlight that can be inop on startup but with a slight tap on the light it comes on. I replaced the bulb. Sometimes at startup it comes on. Other times not. Could there be a short somewhere. Thanks ahead

[Brian Carlton]

You don't have a short.

But, I'd bet the connection pins in the plug to the back of the headlight are not in good shape. Pull the plug from the headlight and you can probably disassemble it to clean the pins. Make sure the pins go back in the same slots.

[iceman3876]

Originally Posted by Brian Carlton

You don't have a short.

But, I'd bet the connection pins in the plug to the back of the headlight are not in good shape. Pull the plug from the headlight and you can probably disassemble it to clean the pins. Make sure the pins go back in the same slots.

Thanks so much Brian. I will take it apart and clean the pins as you've said...

[rg2098]

My W123 does the same thing. I have a broken wire somewhere in the harness from the light back about 6 inches. Right now its ziptied to something nearby that holds it tight in a working postition.

[P.E.Haiges]

Iceman,

First some electrical terms:

When something electrical doesn't work, it usually an "open" or open circuit which means there is lack of continuity and electrical current can't flow. This can be either in the "hot" or ground side of the circuit.

A short is a condition where there is no resistance so a very high current flows in the circuit. If the circuit isn't protected by a fuse or circuit breaker, nasty things will happen: melted wire insulation, burned off wires and possibly a fire.

Getting to your problem: MB uses separate fuse to each head light filament. Therefore it could be a fuse that has corrosion on it that is causing your head light to work intermittantly. Happened to me.

Look on the fuse list and find which fuse goes to the non working headlight. Remove that fuse and scrape the corrosion from the fuse connection and the fuse holder if necessary and replace the fuse. If this doesn't work, you will have to check thru the circuit with a voltmeter.

I still can't figure why MB uses those flimsy fuses when glass encased, chromed ends, Buss type fuses are much more reliable.

P E H

[Brian Carlton]

Originally Posted by P.E.Haiges

Getting to your problem: MB uses separate fuse to each head light filament. Therefore it could be a fuse that has corrosion on it that is causing your head light to work intermittantly. Happened to me.

"A slight tap on the light" will allow it to illuminate. Unless you believe that a slight tap up in the front of the vehicle can vibrate a fuse in the box, the fuse is not the culprit here.

[P.E.Haiges]

Brian,

You are probably right, I missed the part about tapping the light. But the rest of the post should have useful information.

P E H

[Brian Carlton]

Originally Posted by P.E.Haiges

Brian,

You are probably right, I missed the part about tapping the light. But the rest of the post should have useful information.

P E H

I agree, wholeheartedly about the fuses. But, in this case, he has a problem other than the fuse.

[P.E.Haiges]

Brian,

Yes, I agree that the problem of the open circuit is near the head lamp.

P E H

[barry123400]

However the socket that gives tension to the pin contacts should be looked at carefully as well. Sometimes the transmitted current does some damage to the plug because a slightly higher resistance point existed there. Seen it on a few different car brands. Even changes the colour of the surrounding plastic to some extent if it is a really high resitance connection and created lots of heat. Yes a tap may restore a shakey contact point like that.