X164: One foglight works but there are two working bulbs

[Watchman]

Today is the first time I've had chance to sit on the drive and "play" with my car since collecting it last weekend.

It has a full compliment of exterior lights including rear foglights left and right. But only the right one works. The left one has both wiring and a bulb though, and I swapped the bulbs over to confirm both work.

On Merc forums, there's a suggestion the passenger side one is deliberately disabled. Could that be true? If so, might it only be a virtual switch in the software needed to turn it on?

Or a fuse (haven't checked yet)?

Anyone noticed similar?

[JimmyR1]

Not sure with MB - have never checked on mine - but I know on current VWs (or Golfs at least) there is only 1 rear foglight. The corresponding circular light in the other rear tail light cluster is the reversing light. Maybe it is a RHD v LHD thing, and/or done to deliberately maximise the area of the tail light cluster dedicated to essential lightning functions like stop lights and tail lighting, and give less space to those functions like reverse and fog lighting that are used comparatively much less often?? I am sure someone more knowledgeable than I will chime in, and while I wait for that to happen I am going out now to check what whether my C class has the same set up.

[Cyb3rDud3]

All cars I've had only have one rear fog light enabled, whilst cosmetically two are visible. My X166 only had one rear fog light.

[Watchman]

Cyb3rDud3 said:

All cars I've had only have one rear fog light enabled, whilst cosmetically two are visible. My X166 only had one rear fog light.

That's interesting that you only had one too.

I mean, there's definitely a foglight on the left side too. A reflector, bulb and wiring. The unit is the mirror image of the right one. The bulb works when I swapped it from left to right.

It must be software. I need to fit a towbar soon so I suspect I'll need something "coded". I will ask about this then.

[Magic919]

I used to have a BMW and thought both should work, like a previous one. There is a school of thought that it is safer illuminating one, as there is little chance of it looking like brake lights.

[Cyb3rDud3]

Watchman said:

That's interesting that you only had one too.

I mean, there's definitely a foglight on the left side too. A reflector, bulb and wiring. The unit is the mirror image of the right one. The bulb works when I swapped it from left to right.

It must be software. I need to fit a towbar soon so I suspect I'll need something "coded". I will ask about this then.

I bet when you switch the headlights to LHD that the other fog light will start to illuminate That way it is clear where the outside of your vehicle is and which way to overtake.

[Watchman]

Cyb3rDud3 said:

Watchman said:

That's interesting that you only had one too.

I mean, there's definitely a foglight on the left side too. A reflector, bulb and wiring. The unit is the mirror image of the right one. The bulb works when I swapped it from left to right.

It must be software. I need to fit a towbar soon so I suspect I'll need something "coded". I will ask about this then.

I bet when you switch the headlights to LHD that the other fog light will start to illuminate That way it is clear where the outside of your vehicle is and which way to overtake.

Ah, you know what, that's a smart suggestion. I used to be able to change the headlights myself on my W164 ML. These headlights aren't the same in the slightest but I should be able to do it unless you need a special tool.

[Watchman]

Minor update...

I've been messing about with LED replacements for the few bulbs I have in my exterior lighting. So far, I've achieved a 33% success rate.

I have tried to replace the front sidelights but I cannot get at them - they are buried to the extent that I'd need Barbie's hands to get at them. I even tried to remove the headlamp assemblies but failed when I couldn't get the assy past the bumper - and I didn't fancy removing that. There is some suggestion I only need to rotate the bulb fittings and they'll pull out. If that's true, I might be able to do that from above. I've not given up yet. Those sidelights bulbs are yellow and are horrible in contrast the white HIDs.

The rear foglight was a bust too. I bought a pair of "CANBUS" red LEDs but the car won't recognise them. THEN I checked the Ebay ad where the explanation went further to suggest if I had a car that was so picky (their words) that even the resistance-corrected LEDs they supply won't work, then they can sell you MORE resistors. I don't want to chop into my loom so I'll leave that for now.

HOWEVER, whilst messing about with the bulbs and LEDs in the rear foglights, I have established that if the car thinks you have a busted bulb in the RHS (the only side that lights up normally, as I explained originally above), then the LHS one lights up.

Curious - wish they'd both just light up. Never mind.


Anyway, there was one success tonight... as I have to reverse up my driveway and we have absolutely no streetlighting where I live, I replaced the reversing bulbs with some powerful LEDs WHICH WORK (hooray). In fact they are quite spectacular, and the fact that clearly GENUINE CANBUS LEDs that my car will accept exist in this world has emboldened me to look again at the rear foglights and the front sidelights this weekend.

Wish me luck.

Edited by Watchman on Friday 10th February 19:16