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Discussion Starter · #1 ·
Happened to have my rear fog lights on and got out of the car and realized my right one was out. Took the cover off inside and found a blank where the light should be. Is this normal or did someone screw up?
 

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Discussion Starter · #2 ·
Never mind. Checked the owners manual (should have done that first) and it is apparently normal.
 

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There's only one rear fog light if I remember correctly! I use the front and rear fogs a lot of times but have never actually seen how they look from the outside.
 

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European spec. We think of fog lights as appropriate for driving in fog, i.e. lighting the road. They're actually more parking lights--either when you pull off the road or park against a curb--so oncoming cars can see you. They are the same on my MB C300.
 

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Discussion Starter · #5 ·
I generally use them when driving in heavy rain/snow or heavy fog, just didn't realize there was only one. My brain that likes symmetry starts to tweak a little when I only see one light.
 

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I generally use them when driving in heavy rain/snow or heavy fog, just didn't realize there was only one. My brain that likes symmetry starts to tweak a little when I only see one light.
That's sort of the logic behind the single rear fog light - to stick out to drivers behind you.
 

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That's sort of the logic behind the single rear fog light - to stick out to drivers behind you.
I guess that would make some sense, but I've never seen this formally stated anywhere...
And, as is inferred above, it's not just Volvo that has the single bright "fog light" on the left rear side...
 

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I guess that would make some sense, but I've never seen this formally stated anywhere...
And, as is inferred above, it's not just Volvo that has the single bright "fog light" on the left rear side...
And it's only the US. In Europe the cars have fog lights both taillights - you can see how US bound cars are modified. I think it's a NHTSA rule.
 

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And it's only the US. In Europe the cars have fog lights both taillights - you can see how US bound cars are modified. I think it's a NHTSA rule.
Not so sure about that. This goes back several years but during my 6 years living in France in the 1980's, the Peugeots and German Fords I drove all had single fog lights in the rear. That dual side set-up with a plug for one side may be there to meet specs for right hand drive cars.
 

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Much better single sided. You notice that it's fog lights instead of broken Volkswagen taillights;)

Sent from my Pixel 2 XL using Tapatalk
 

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Discussion Starter · #11 ·
I thought someone screwed up and forgot to install the wiring harness. Manual pretty clearly states it’s a single light in the drivers side only. As someone suggested, the blank is there so they can wire the same light for right hand drive vehicles. Attached is the manual for a UK S90
 

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And it's only the US. In Europe the cars have fog lights both taillights - you can see how US bound cars are modified. I think it's a NHTSA rule.
Uhm no. I live in Sweden and both my current V90 and my previous V50 had only ONE rear foglight. Same goes for many other brands over here. I've seen more cars with one foglight in the rear rather than two, that's for sure.
 

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I don't think the NHTSA says anything about rear facing foglights.

My memory for the EU is that the requirement is that cars be equipped with at least one rear facing foglight on the driver's side of the vehicle, and that that light is a dedicated foglight.

So, some manufacturers build with just the one light and vary which side based on whether the car is LHD or RHD. Others just include two lights (some Audis, some Toyotas) to cover their bases.
 

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They are basically rear position markers, but you all probably knew that :)
That's actually a different light than the rear fog lamp. Position light is what we used to call "running lights".
 

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I don't think the NHTSA says anything about rear facing foglights.

My memory for the EU is that the requirement is that cars be equipped with at least one rear facing foglight on the driver's side of the vehicle, and that that light is a dedicated foglight.

So, some manufacturers build with just the one light and vary which side based on whether the car is LHD or RHD. Others just include two lights (some Audis, some Toyotas) to cover their bases.
You're right - it was the UN.

https://www.unece.org/fileadmin/DAM/trans/main/wp29/wp29regs/2013/R048r9e.pdf
 

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They are basically rear position markers, but you all probably knew that
That's actually a different light than the rear fog lamp. Position light is what we used to call "running lights".
Perhaps. I think the rear fog light helps mark the drivers side/position in poor visibility. Tomato/Tomato
Then again I've never had a vehicle with the rear fog light.
 

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The main reason manufacturers choose to only install one instead of two fog lights is to make sure the lights aren’t confused with brake lights.

Back in the day (when filament bulbs were the norm), brake lights and rear fogs both required 21w bulbs, so they would have the same light output as well as the same color.

Additionally, Europe didn’t mandate CHMSLs (3rd brake lights) until 1996, and you can see why a manufacturer would avoid placing two additional red lights on the rear of a car that could be switched on permanently.

These days, the risk of confusion is a little less pronounced but given the intensity of the light, still present. And since it’s only meant to alert other drivers that someone is driving in front of them, one light is simply sufficient to fulfill that purpose.
 

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Discussion Starter · #20 ·
The main reason manufacturers choose to only install one instead of two fog lights is to make sure the lights aren't confused with brake lights.

Back in the day (when filament bulbs were the norm), brake lights and rear fogs both required 21w bulbs, so they would have the same light output as well as the same color.

Additionally, Europe didn't mandate CHMSLs (3rd brake lights) until 1996, and you can see why a manufacturer would avoid placing two additional red lights on the rear of a car that could be switched on permanently.

These days, the risk of confusion is a little less pronounced but given the intensity of the light, still present. And since it's only meant to alert other drivers that someone is driving in front of them, one light is simply sufficient to fulfill that purpose.
It's still effective when someone is tailgating you
 
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