One rear fog light on

[bigjobby01]

I have a 1997 C200, when I turn my headlights on, one of my rear fog lights come on, when I pull the headlight switch the other one comes on, press it and only one goes out. All other lights are OK. Any ideas where to start??

Many thanks

 

[Blobcat]

In the first instance I would check all the connectors and earths on the FOG light that is staying on. Probably a faulty connector/earth.

 

[jberks]

I agree with Blobcat. Using a 12v tester, first check that there is power where it should be and not where it shouldn't, then check the earths. Check one side and compare to the other. This issue is normally caused by the tail light having a poor earth and back feeding through something else, in this case, the fog light.

 

[Myros]

just a thought

but aren't we only supposed to have one rear foglight.

 

[jberks]

Some do, but I believe his problem is it coming on with the tail lights.
Ah - just had a thought....
Are you sure its the fog light and not just the stop light bulb upside down? You'd have one normal and one bright tail light that will look just like a fog light....

 

[C220GJS]

Some do, but I believe his problem is it coming on with the tail lights.
Ah - just had a thought....
Are you sure its the fog light and not just the stop light bulb upside down? You'd have one normal and one bright tail light that will look just like a fog light....

Good thinking jberks , but I can't see how you could put these bulbs in the wrong way round unless you really forced it ,as along with the pins being at different heights they are also offset radially, that is they are not 180 degrees apart, more like 210/150 degrees.
I found this out when my daughter needed a brake/tail bulb for her Fiat and couldn't understand why my spare wouldn't fit in the bulb holder , after a bit of head scratching I noticed the different orientation of the pins.
I have honestly never noticed this before, is this a unique bulb to Mercedes ?

 

[Myros]

industry standard

to prevent people doing just what your daughter tried to do. they can be foeced in, and all too often are. Worth a shufti just to rule it out.

 

[jberks]

Yes - I discovered the offset pin ("Idiot proof") bulbs with my 210 but I wasn't sure when they introduced them. I can't remember replacing the bulbs on my C so I thought they may have been a more recent development.
If it's been around for a long while, its probably not the problem, though as you say, some people don't twig and force them. If not, then back to the circuit tester and wire wool!

 

[bigjobby01]

Thanks for the speedy replies, apologies for my delay. The bulb in question dos not have the bayonets "off set", they are level. All the bulbs are clustered in a plastic surround with a "plug" for all the wiring. I have unplugged this and cleaned the pins. I have turned the bulb around and swapped it for a new one, still the same. It isnt the break light, that is the top one, it is the tail light with the fog light?????