Mercedes Benz E-Class W124 (1985 - 2000) - 92 2.3 W124 odd bulb failure

Honest John Back Room » Technical matters
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Thu 17 Jul 2008 22:35
92 2.3 W124 odd bulb failure - FrankSm
Hey folks

I have an odd issue with one of the front fog lamps right now ? don?t know if US cars have these, but they are the inboard lamps in the front lamp units. Anyway, one is getting a healthy 12V, the other shows between 6 and 9 volts ? upon plugging a good bulb the voltage goes down to zero. It?s as if any load on the circuit brings it down. Bulb-failure warning is lit up the whole time. The earths there are sound, I tested it with a new earth lead to a test bulb; the cabling is sound too. Problem is not the bulb, I have swapped in known-good bulbs

I need to trace things back to the ?lights control unit? - must be under the dash ? Fuses are good too ? the number-4 fuse servers front fogs as well as the single rear fog.

Smells like a bad earth, but apparently not !

Cheers

Frank
1992 230CE W124
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Thu 17 Jul 2008 22:43
92 2.3 W124 odd bulb failure - Number_Cruncher
You have a poor connection somewhere. There's a multiplug on the back of the headlamp unit, and the bulb failure unit is in the relay box behind the fuse box.



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Thu 17 Jul 2008 23:45
92 2.3 W124 odd bulb failure - FrankSm
Thanks - I know exactly what you're talking about, there is a box there behind the fusebox. What an awful place to put it - right under the windscreen ledge/bonnet hinge :-O
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Fri 18 Jul 2008 10:41
92 2.3 W124 odd bulb failure - Peter.N.
Agreed. Sounds like an earth connection, effectivly putting the two lamps in series.
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Fri 18 Jul 2008 11:52
92 2.3 W124 odd bulb failure - SpamCan61 {P}
I had a very similar problem on an Omega ( in the midlle of the very, very dark New Forest at 6 a.m.) Turned out the crimp connection bettween the lucar(?) connector and the feed cable had corroded under the plastic shroud, and was producing significant resistance in the circuit. With no current drawn there was still 12V on the connector, this dropped to stuff all when the lamp was put in circuit.

Not the kind of subtle problem I wanted to investigate at that time and place!
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