W124 Rear Fog Light

[Molesworth2]

Took my E220 for MoT, passed on everything except rear fog light! Bulb is good, fuse is good, and the indicator light on the switch in the cabin illuminates when switch is pulled out. But there is no current at the wire at the rear panel... (tested with multimeter).
I realise there must be a fault in the wire somewhere, are there any obvious weak points where failure is likely eg where the wire enters the boot?
Many thanks for any advice.

PS post-MoT, I was looking at the problem and the bulb suddenly started working again! This morning I was all set to go back for the re-test, when a final check showed it had failed again! Very frustrating.

 

[stwat]

Check the fuse associated with the fog light. It may look okay but can be partially broken or even dirty/corroded on the contacts.

 

[Molesworth2]

Fog Light Fuse

Thank you, I have spares so will fit new one to see if that helps, but front fogs work & I think they are on the same circuit? Anyway, thanks for suggestion I will now check...

 

[television]

look at the bottom and you can see it goes to the headlamp circuit

http://www.autolib.diakom.ru/CAR/Mercedes-Benz/1994/E320/SYSTEM WIRING DIAGRAMS/4932.pdf

No fuses for this I think

http://www.autolib.diakom.ru/CAR/Mercedes-Benz/1994/E320/SYSTEM WIRING DIAGRAMS/4935.pdf

 

[Bolide]

Corroded or loose bulb holder

Nick Froome

 

[EmilysDad]

Is there a towbar fitted? Some towbar wiring will turn the car's rear fog light off when the trailer/caravan s plugged in ...... maybe an iffy micro switch in the 12N socket

 

[Molesworth2]

None the wiser...

Many thanks to all suggestions and quick responses.
I put a new fuse in - still no light.
Then went out for quite a long drive with heater on; after 30 minutes I stopped, thought I'd check the light and it came on! The only difference between earlier in the morning was that the car had warmed up (including inside) - ?could it that some condensation somewhere was shorting out a wire?
Anyway, then dashed to MoT station where light still worked, got new certificate (phew), drove home at the moment it is still working...

 

[television]

I think just a bad contact on the bulb, it needs some switch cleaner on it of the non drying kind