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The first diagram is legal in most states --- the second is NOT. Second is great for making a clean get away from a stick up at your local Tom Thumb or WaWa at night.  Believe the code says the front and rear running lights must be on when the fog lights are on.  In the fog you'd surely want the rear running lights on - plus you don't want to leave them on when car is parked.

Road Rule 217 states that drivers must not use front or rear fog lights unless driving in fog or other hazardous weather conditions that cause reduced visibility. They must be switched on separate from the main beam (high beam) and dipped beam (passing) headlightsJan 5, 2016

Last edited by WOLFGANG

I know that when I drive my Fiat Abarth at night I always turn my fog lights on since they provide more near light and also because they look cool.  Doubt anyone would ever get pulled over for burning fog lights with low beams regardless if there is fog or not.  But it sounds like using fog lights alone during the day as day time running lights may not be a good idea.  Maybe diagram 1 is the way to go.  I've got a buzzer to tell me if I leave my lights on.  If I used diagram 2 the buzzer would not function if fog lights were left on.  If the fog lights were left on during the day the battery could be drained.  Another reason to go with diagram 1.  Thanks Wolfgang.

This is the fog light wiring harness I bought.  I really only have one concern.  The red (+) wire coming from the connector to the power switch.  I'm assuming that I can run it to the battery with another in line fuse.  And if I do should I use another 25A fuse box?  This would allow the fog lights to run independently from the ignition.  Or I guess I could run this directly to my main fuse box and tie it into a fuse dependent on the ignition being on.  Any particular fuse be better for this?  Thanks

Or I guess I could hook it to the (+) wire from one of the low beams.  But then the fog lights could only be used when low beams are on.  I think I would like them independent from headlights.



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Last edited by 550 Phil

It looks good to me ... Relay is that box right?  I would call Henry to get a seperate switch to match yours and install on the dash as a seperate switch ... on the left side of the dash. 

It should go from the Battery Positive via a seperate in line fuse to the Relay then the Relay to each of the lights. Then the Switch operates the relay but only if the ignition  key is in active mode.  That is how Henry wired mine essentially. 

On Bridget (my fake MG TD) I wired a single Lucas fog light separately from the headlight circuit. One night a few years ago, after an evening meal with the boys, my headlight switch bit the dust as I entered a hairpin highway interchange. I flipped on the fog light and was able to negotiate the curve and make it home.

I do not use the fog as a running light. I run low beams during the day, But as emergency illumination it was and remains a definite plus.


@550 Phil posted:

...I really only have one concern.  The red (+) wire coming from the connector to the power switch.  I'm assuming that I can run it to the battery with another in line fuse.  And if I do should I use another 25A fuse box?...


Phil, that wire is the 'trigger' circuit for the relay, so it doesn't carry heavy current, and needs only about a 1-amp fuse.

The current for the lights goes through the 'Safety Fuse Box' in your diagram, which is why that has a 25 amp fuse (and heavier gauge wiring than the switch).

If you want to control the fogs independently of the headlights, run that wire to any circuit in the fuse box. If you want the fogs to be inoperable when the key is off, you could also run that wire to the accessory contact of the ignition switch (through a small inline fuse holder).


It must be a few years ago. Cory looks about the same today, but the rest of you look a bit younger there.

For ALWAYS HOT fog lights and other accessory stuff, I like this simple 3 wire method.


If you want the relay controlled from ignition/accessory or other power source(headlights) DON'T splice #30 and #86 together. Run #30 to constant hot and run #86 to your other switched source(ignition/accessory/low beam).

ALWAY fuse the heavy feed wire(#30) as close to the source as possible. This protects the entire circuit.


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@DannyP posted:

Legally, driving lights are only allowed to be on when using high beams in the USA. I believe they are supposed to be connected to the high/low dimmer, so they can't remain on all the time.

No, I don't know of anyone who got a ticket for this.

Actually it's the opposite.  They're only allowed on with low beams.  Most (like my BMW) will cut off the driving lights if you turn on high beams.

Actually it's the opposite.  They're only allowed on with low beams.  Most (like my BMW) will cut off the driving lights if you turn on high beams.

Or is that fog lights? I can't remember. I always thought driving lights went on with high beams but fog lights were allowed on low beam only.

My truck has clear fog lights that go off with the high beam. Their cutoff pattern is very low, but I've not measured it.

The real gist of it is aux lights need to be mounted BELOW the regular headlights(between 16 and 42 inches above ground) and cannot be above a 42 inch high beam pattern at 75 feet.

The other thing is you are not allowed to blind oncoming drivers which is why they should be hooked to the high beam. There's a car coming, you dip your high beams, and your aux driving lights shut off, NOT blinding the poor shlub coming the other way. But maybe I'm wrong.


I've been thinking this through a little more.

If the driving lights are wired so you can turn them on whenever you want, that means the driver has to know what the law is and drive accordingly.

But this is Amurica, dammit. Isn't it the car maker's responsibility to know the law and to keep me safe? How am I supposed to concentrate on my phone when I'm constantly being distracted by all these driving decisions?

I sense a great class-action lawsuit in the works here.


Last edited by Sacto Mitch


I got fed up with myself, leaving the lights on when parked.

I use the headlights in daylight only occasionally - usually early morning hours or driving on roads that are alternately in deep shade and bright sun, so I was always forgetting to turn them off.

I wired all the relays (for everything, even the cooling fan) through another relay that's powered from the accessory contact on the ignition. That way, I can still use stuff when parked, but once the key is in my pocket, nothing can drain the battery.

Last edited by Sacto Mitch

I totally agree with Danny, and am 180º away from Lane's position.

Fog lights come on with low beam and cast a light pattern horizontally with a cut-off line no higher than 36" at 50' from the car to prevent blinding of oncoming drivers.  Technically, then can be left on when switching to high beam, but most car makers switch them off when high beams are on.

Driving lights are only on with high beam and cast a beam of light as a spot (lots of variations, here) 10' - 15' wide at a quarter mile (yes, there's a federal spec for this).  Lucas once had a driving/spot light that I loved the name of; Their 8" "Flame Thrower"!  I looked like a huge version of a Marshall driving light.

If you have a light that goes off when you switch to high beam, it is a fog or running light.  If it comes on with high beam and is not your standard headlight, then it is a so-called "driving light".

Bear in mind that either of these sold on most dealership cars in the USA pretty much suck at doing their job unless the dealer adds a European version, which is much better.  In Europe, Fog lights are mounted below the bumper to sweep the road immediately ahead of you (out to 75 feet or so) and use their low angle to enhance road shadows.  They also don't reflect much light from fog and snow coming at you, especially if they have amber lenses, because they are aimed horizontally or down.  Many in dealership cars can be left on when the headlights are off to further reduce fog/snow glare and still let you see some of what's ahead.

Driving lights are mounted above the bumper to light the road 1/2 mile ahead so you can see and avoid stuff at speed.  Since they are always clear, they reflect fog and snow like crazy (but you can't see 1/2 mile in fog or snow anyway, so go back to low beam and slow down!)  The only exception to this was the old Perlux lights with the horizontal vanes across the lenses to enforce a light pattern cut-off line as mentioned above.

Last edited by Gordon Nichols
@IaM-Ray posted:

@Michael Pickett

If your concerned about visability you might consider getting the full flashing brake lights and 3rd eye by  I have mentioned before and I keep installing them on every car I buy.

BTW, I once knew a french guy called PIquette

You're(you are) using "your" wrong.(Contraction used)

Your concerns are not mine.(No contraction)

This is how you're supposed to use the contraction.(Contraction)



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