Wiring fog lights. Is this a good idea?

I have a set of LED fog/driving lights that I want to mount but I wasn't sure the best way to power them. I just did the headlight wiring harness upgrade to use the relays with direct draw, and noticed that when I was done the original power feed to the drivers side headlamp is left unused. I was wondering If I could use this to power the led fog lamps? In theory, I would run power from both the high and low beams in the unused drivers side headlamp connector to the fog lights so that regardless of which set of lights are turned on, the fog lights would stay on.

The lights I was going to install have 12 Led bulbs total (6 in each light) with each LED bulb running at 3 watts so I calculate only 3 amps draw when they are on, which doesn't seem like a lot to take from the unused headlight harness.

So.... is this a good idea?

Thanks
Chad

I dont see why it wouldent and I am hoping that someone will correct me if Im wrong. One other thing you might want to look into. In some states it is not legal to run fog/driving lights when your high beams are on, only low beams.

I would wire the headlight connector to another relay's coil and use that relay to power the fog lights.  But you want the relay to come in when you have either the highs or lows on, so you'll need to use a diode from one or the other to the relay's coil or you'll have the lows feeding the highs and vice versa.  (I can diagram that if you need me to.)

Why would I use a relay when you are only pulling 3 amps?  Because 12v x 3 amps is 36 watts, each headlight only draws 35 watts on low.  So you'll be pulling as much wattage as the low beam wires were originally spec'd to do.  And you put the relay harness in because those wires and the switch weren't adequate.

Hi Steve. I'm sure that is a law in many states (or something similar). Luckily I live in Georgia, where you can title, register and drive basically anything with turn signals. It is insane what they allow here.

My neighbor bought a demilitarized Hummer without a dot/epa approved engine and surplus branded title and managed to get it registered and plated by just adding seatbelts. Seriously insane here.

Gary,

Understood.

1. If I can't use the LH headlight connection for power than it seems like it wouldn't make sense to use it for the relay because I'd have to draw power from the battery on the passenger side. If I'm using a relay doesn't it make more sense to just power the relay from the passenger side headlamp using a jumper?

2. I would like to wire it so the driving lights are on regardless of hi/low beam selection. Given that, does it still make sense to use the headlight connection to trigger the relay or is there a "better" place to draw power for the relay? If the headlight is the best place, can you please explain your comment regarding the required use of a diode? I don't quite follow what you're suggesting.

Thanks
Chad

I agree that you want to put the relay on the passenger's side.

As for the diode, do something like shown below.  Otherwise, if you just tie the high and low beam wires together you'll have both high and low beams on at the same time.

Having referenced "what does a diode do" on my googlebox after looking at your picture, I now understand it's a one way circuit. A diode on both of those lines will prevent the triggering of both hi/low simultaneously when I splice them together prior to affixing them to connection 85 on the relay. Thanks again.

old55pete wrote

I dont see why it wouldent and I am hoping that someone will correct me if Im wrong. One other thing you might want to look into. In some states it is not legal to run fog/driving lights when your high beams are on, only low beams.

My 02 Durango turns off the driving lights when the high beams come on that I think is stupid.
No one else is around when the high beams come on so whats the big deal?

I also have not heard its illegal to run driving / fog lights with high beams.
Is then there should be a lot of tickets given out to the rednecks that put them LED light bars on the front of cars & trucks as they do blind on coming traffic.
They are also on the EMS trucks down here.

Also if it was illegal in some states the lights you can buy and add on like the LED light bars would say something on the box or paper work.
Only thing I did see on my K C Lites were not for street use and the only time I used them was in VT late at night on back roads going to a buddies cabin. Other wise the covers were on them.
Dave ----

I have my fog lights wired so they shut off if the high beams are on (fog light switch wired to 87A of the high beam relay)
Having the high beams on in dense fog is self defeating.

If they are driving lights you probably want them on with the high beams so Gary's isolator harness is the simplest route, and using the unused drivers side headlamp socket from the factory harness is probably the WTG.

I wish Radio Shack was still in every corner of the country when little projects like this pop up.
Trying to source two diodes costs more in time and shipping than they do these days.

ArdWrknTrk wrote

I have my fog lights wired so they shut off if the high beams are on (fog light switch wired to 87A of the high beam relay)
Having the high beams on in dense fog is self defeating.

If they are driving lights you probably want them on with the high beams so Gary's isolator harness is the simplest route, and using the unused drivers side headlamp socket from the factory harness is probably the WTG.

I wish Radio Shack was still in every corner of the country when little projects like this pop up.
Trying to source two diodes costs more in time and shipping than they do these days.

Yep can't just go buy one or two, you have to buy a box of 1000 online.

That's not true.
Go to Digi-Key, Mouser, Newark or others and get as few as you need.

SMD's on a spool perhaps not, but anything with legs is sold individually

FWIW, I ordered a set of these (4 pack means that I'll have 3 in a drawer for the next 30 years):

https://www.amazon.com/gp/product/B0002Q81Y4/ref=ppx_yo_dt_b_asin_title_o03_s00?ie=UTF8&psc=1

I'm just using a universal relay like the ones in the heavy duty lighting harness so I don't need a variety of spares.

I agree that there are situations where you would want independent control of fog/driving lights vs the headlights and that is a far better way to do it. That way you could not only conform with the law but light correctly for conditions. This way of doing it is just a personal preference because Georgia doesn't get fog, and when it does it isn't the "thick as soup" variety.