Correct way to Wire Rear Fogs?

Hamilton Felix

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Is there a standard or even traditional way to wire a rear fog light? I was thinking of options:

1. Completely independent circuit, manually on or off.

2. Completely independent switch, functions with low beams, as do front fogs.

3. Tag onto a front fog circuit, so functions when front fogs and low beams are on.


I'm leaning toward #2 with a distinct indicator so I don't forget it. I do tend to wire most of my auxiliary lights with double throw, center off switches, so I have "On-Off-Auto," with manual "On" being for aiming, testing, etc. while "Auto" is for normal use, driving lights with high beams, fog or auxiliary low beams with low.

I just realized I've no experience with the correct way to set up a rear fog. :confused: I realize it's important in thick fog, but should not be forgotten or left on when there is no fog. European forum members probably know the answer. But I'll appreciate any advice I receive.
 

smokinbasser

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Just thinking here but there might be DOT laws prohibiting this due to vehicles behind you thinking a car is about to hit them and taking evasive action right into a head on collision. I would worry about what is in front of you rather than behind you. Just my opinion!
 

fastgun

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It would be personal preference in many places. As an FYI California has the requirement that rear fog(s) may be turned on only when headlights are on and there must be a switch to turn them off while headlights are still on. This state also specifies an amber pilot light to indicate when the rear fog is turned on. Most states are silent and the others that I have read simply state that rear fogs are allowed. As always check your state.
 
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Alaric Darconville

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Just thinking here but there might be DOT laws prohibiting this
Rear fog lamps are not Federally-regulated; their use is regulated by States.

due to vehicles behind you thinking a car is about to hit them and taking evasive action right into a head on collision.
A rear fog lamp is visible far enough back that the approaching driver simply needs to slow down, not swerve. It's not like a rear fog lamp is projecting white or yellow light, making it look like a potential head-on collision, anyway. (Perhaps you were thinking by "rear fog" it was meant that it was a standard fog lamp such as would be used for forward lighting, just mounted on the back of the car. No, a rear fog lamp is a *red* lamp with an output pattern not at all like that of a normal fog lamp. See here-- and there are also other threads here about rear fog lamps.)

I would worry about what is in front of you rather than behind you. Just my opinion!
'Cept that what's behind you could rear-end you, and even if you're not at fault (in most States you typically aren't) it's a big ol' hassle, and a rear fog lamp is effective at preventing rear-ending accidents in heavy fog. The guy behind you has his front fog lamps on, and is going 80mph in a nominally-65mph zone with fog calling for 25mph. His front fog lamps aren't going to help him see you better, nor would your own front fog lamps help you see the car in front of you better-- your rear fog lamp DOES let the people behind you see you better.

Also, in UNECE signatories, front fog lamps are *optional*, and rear fog lamps are *required*, which highlights the efficacy of rear fog lamps.
 
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Alaric Darconville

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Is there a standard or even traditional way to wire a rear fog light?
Follow UNECE R48.

UNECE R48, 6.11.7.*, .8
6.11.7. Electrical connections
These shall be such that:
6.11.7.1. The rear fog-lamp(s) cannot be switched on unless the main beams, dipped-beams or front fog-lamps are lit;
6.11.7.2. The rear fog-lamp(s) can be switched off independently of any other lamp;
6.11.7.3. Either of the following applies:
6.11.7.3.1. The rear fog lamp(s) may continue to operate until the position lamps are switched off, and the rear fog lamp(s) shall then remain off until deliberately switched on again;
6.11.7.3.2. A warning, at least audible, additional to the mandatory tell-tale (paragraph 6.11.8.) shall be given if the ignition is switched off or the ignition key is withdrawn and the driver's door is opened, whether the lamps in (paragraph 6.11.7.1.) are on or off, whilst the rear fog lamp switch is in the "on" position.
6.11.7.4. Except as provided in paragraphs 6.11.7.1., 6.11.7.3. and 6.11.7.5., the operation of the rear fog lamp(s) shall not be affected by switching on or off any other lamps.
6.11.7.5. The rear fog lamp(s) of a drawing motor vehicle may be automatically switched off while a trailer is connected and the rear fog lamp(s) of the trailer is (are) activated.

6.11.8. Tell-tale
Circuit-closed tell-tale mandatory. An independent non-flashing warning light.
 

LeanBurn

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I would put in a relay with the front fogs to automatically come on when the fogs do.
 

Handon11

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I'm in North America, and I drive a Saab and the rear fogs are completely independent from any forward facing lights - fogs, lows, or highs.
 

Alaric Darconville

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I'm in North America, and I drive a Saab and the rear fogs are completely independent from any forward facing lights - fogs, lows, or highs.
:welcome:

Which is a rather odd way to set it up-- sounds like someone thought it'd be more appealing to the 'Murricans.

If conditions are right for a rear fog lamp, they're right for your other position lights/sidemarkers and all that.
 

Handon11

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I guess I should rephrase that: independent from front fogs and highs. My running lights and low beams are just always on, as a factory setting - cannot turn them off except when my car is off. But yes, otherwise they are on a line all on their own.
 

Hamilton Felix

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Interesting, Handon11. My last Saab was a 1978 99 Turbo (unless you count former wife's 1982 900 Turbo). Loved it (well, loved both, wife totalled first one but I found another). My headlights could be left on, and would go on and off with the key (bad to start car with lights on and subject them to low voltage then the high charge surge). I see now we've progressed to "no choice." My 2007 Corolla does not really have an "off" position, only "auto." It decides when the lights should be on. I'm old fashioned and I want to control things myself. Saab was wonderfully weird before it became a "global car" like all the rest.


Thanks, Alaric. That spells it out. I like that "main beams, dipped-beams or front fog-lamps" line. The requirement in 6.11.7.3.2 for an audible when you pull the key and open the door is interesting. I guess best course is to use the "accessory" circuit on the switch as permissive, along with headlights. Or better yet, just go with 6.11.7.3.1 make rear fog dependent on position lights.

I'm debating whether there would ever be an advantage to rear fog while stopped with only marker lights on. Perhaps, if it has more range then four way flashers. But I'm going to have the yellow four ways on if I have to stop along the highway in heavy fog. I don't think I'll worry about it.



I most certainly agree with the tell-tale reminder light. One really hates to turn on any sort of light and forget it, especially on the rear of a vehicle.


I suppose some legal research is in order. Getting a straight answer from Washington State, and especially its Commission on Equipment, can be a challenge. But some quick rereading of the latest RCW 46 (our vehicle code) and perhaps a letter directly to the State Patrol should provide answers.
 

Alaric Darconville

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The requirement in 6.11.7.3.2 for an audible when you pull the key and open the door is interesting.
For your purposes, I suppose that could be optional so long as you then remember you still have to turn the switch off and back on again to reactivate the lamp.

I'm debating whether there would ever be an advantage to rear fog while stopped with only marker lights on. Perhaps, if it has more range then four way flashers. But I'm going to have the yellow four ways on if I have to stop along the highway in heavy fog. I don't think I'll worry about it.
The four-ways should be visible about as far back, maybe even more so, and the flashing would make them noticeable. I'd turn it off if I were pulled over and using the hazard flashers, myself.

I most certainly agree with the tell-tale reminder light. One really hates to turn on any sort of light and forget it, especially on the rear of a vehicle.
Particularly something like a rear fog lamp-- that'd get obnoxious quickly in clear weather.

I suppose some legal research is in order. Getting a straight answer from Washington State, and especially its Commission on Equipment, can be a challenge. But some quick rereading of the latest RCW 46 (our vehicle code) and perhaps a letter directly to the State Patrol should provide answers.
Certainly, any car that was equipped at the factory with rear fog lamps, and certified by the manufacturer as conforming to FMVSS 108, is allowed to have the lamp(s). But the USE of the lamps would be up to States, of course. This is part of the reason why you want them wired sanely (so they aren't just on willy-nilly) and then, of course, operated sanely. The RCW is written more to indicate which lights are *required* with scant few proscriptions of lights, and those usually deal with blue light or flashing lights and the like.
 

Hamilton Felix

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Good points, all. And thanks for the help. Maybe it was those years doing the vol. fire/EMT thing, but I have a strong aversion to being run over. ;) I usually carry some sort of small amber beacon or flasher, just in case I have to stop at an accident or tree across the road.

I still remember a VERY close call many years ago, when I (being young, foolish and eager to see a girl) had a 6 cylinder full sized1962 Plymouth nearly flat out on a foggy highway, just barely thought I saw tail lights, then an instant later "OH S*&$!" I jumped on the brake for all I was worth. The car ahead had low beam headlights, but only his rear reflectors, both tail lights dead. I still don't know how I missed rear ending him, but it was ... educational.

I do think the traditional old Eurpoean rear fog, a red light hanging lower than the tail lights, between center and driver's side, makes a lot of sense in heavy fog. Too bad I can't still order a Cibie Series 35 rear fog with 55 watt H2 bulb. :D
 

Bdm82

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My Q5 has them. They require lights to be on, then they are controlled independently, just like the front fog lights.

I have used them a few times in really bad visibility; they just make the back of the vehicle a little easier to see. (They are red, so if you didn't know what you were looking at you wouldn't know they are "fogs".)
The other use I've found is to communicate with a driver who is failing to maintain proper following distance. Power cycling the rear fog lamps sends a communique without altering the speed of either vehicle (as triggering brake lights would do).
 
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