Fog lights on with High Beams
03-09-2007, 11:57 PM
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Fog lights on with High Beams
Fog lights on with High Beams
It took me a while but I figured out how to keep the fog lights on when the high beams are turned on.
My first attempt was by hooking up, directly, a wire from the 12V pos. side of the high beam wire directly to the fog lights …. No way. Lights flickered and this just wasn’t right.
Then after looking at my wiring diagram, I realized that the fog lights go off not because of a lack of power but because of a lack of a ground and it is the Body Control Module (BCM) , a computer, which controls among other things, when the fog lights are grounded or not.
The BCM turns off the fog lights at a few times, 1 when the ignition key is off and the headlights are off ( I like this because it means I can’t accidentally leave the fog light on ).
It also turns them off when the fog light switch is pressed to the off position and when the high beams come on.
So I liked some of the factory features, but I do not like the fog lights going off when I turn the high beams on.
I don’t know about you but when I turn my high beams on I want more light, not less.
All I needed to do then was ground the wire that goes to the BMC … which I did, but only to find that the fog lights say on all the time, no way to turn them off, so this was no good either.
Then it hit me, all I really need to do was ground this wire when the high beams came on and leave it alone all the rest of the time, a selective ground, so this is how I did that.
Step 1
A while ago I got and installed this wiring harness from Competition Limited to control my headlights. I liked the fact that the Competition Limited http://www.compltd.com/compt.htm harness (WR 9005\6A) has larger wires than the factory so there is no problem using higher wattage bulbs and that it takes 12V pos. power straight from the battery, or in my case the alternator. This helps to prevent voltage loss which means dimmer headlights. I also liked the fact that the harness can and was modified to keep the low beams on when the high beams come on.
So after I installed this harness I had four headlights on when I turned on the high beams, works great, but the fog lights would go off when the high beams came on.
Installing this wiring harness left the High and Low beam factory wires on the passenger side, not hooked up to anything, so they were left dangling.
Step 2
I purchased a PAINLESS WIRING relay part # 30802 not because I wanted the kit, I just really wanted the relay and I knew this kit had it.
I also bought a Male 9005 socket to plug into the empty factory high beam plug on the passenger side of the car.
This would power my relay, making the relay switch ON when the high beams came on. Two wires from the headlight high beam to the coil inside the relay.
I then found the key wire. On my 99 C5 there is a wire that comes off and under the Micro Fog Light Relay #39 which is located in the fuse box next to the battery. It is a dark green wire with a white stripe that goes to the BCM …. This is the all-important grounding wire that the BCM turns off at the most inopportune time.
I “T’ed” off this wire and connected it to the switch able side of the relay and then to a good ground so that when the high beams came on, it would power my new relay and give the fog lights a ground that the BCM had just turned off.
I used no fuses with my new relay because it is powered by the factory high beam circuit, which already has a fuse.
So that’s it, fog lights now stay on when the high beams come on as well as the low beams, 6 lights. I could have put in a toggle switch in to turn off my new relay if I ever wanted the fog light not to come on with the high beams, but I’ll leave that for later if I ever need it. As it is now, when the high beams come on, I have no control, all 6 lights come on, which is fine, like I said, when I turn on my high beams I want light !!
Otherwise the fog lights work just like the factory setting.
Hope this helps.
It took me a while but I figured out how to keep the fog lights on when the high beams are turned on.
My first attempt was by hooking up, directly, a wire from the 12V pos. side of the high beam wire directly to the fog lights …. No way. Lights flickered and this just wasn’t right.
Then after looking at my wiring diagram, I realized that the fog lights go off not because of a lack of power but because of a lack of a ground and it is the Body Control Module (BCM) , a computer, which controls among other things, when the fog lights are grounded or not.
The BCM turns off the fog lights at a few times, 1 when the ignition key is off and the headlights are off ( I like this because it means I can’t accidentally leave the fog light on ).
It also turns them off when the fog light switch is pressed to the off position and when the high beams come on.
So I liked some of the factory features, but I do not like the fog lights going off when I turn the high beams on.
I don’t know about you but when I turn my high beams on I want more light, not less.
All I needed to do then was ground the wire that goes to the BMC … which I did, but only to find that the fog lights say on all the time, no way to turn them off, so this was no good either.
Then it hit me, all I really need to do was ground this wire when the high beams came on and leave it alone all the rest of the time, a selective ground, so this is how I did that.
Step 1
A while ago I got and installed this wiring harness from Competition Limited to control my headlights. I liked the fact that the Competition Limited http://www.compltd.com/compt.htm harness (WR 9005\6A) has larger wires than the factory so there is no problem using higher wattage bulbs and that it takes 12V pos. power straight from the battery, or in my case the alternator. This helps to prevent voltage loss which means dimmer headlights. I also liked the fact that the harness can and was modified to keep the low beams on when the high beams come on.
So after I installed this harness I had four headlights on when I turned on the high beams, works great, but the fog lights would go off when the high beams came on.
Installing this wiring harness left the High and Low beam factory wires on the passenger side, not hooked up to anything, so they were left dangling.
Step 2
I purchased a PAINLESS WIRING relay part # 30802 not because I wanted the kit, I just really wanted the relay and I knew this kit had it.
I also bought a Male 9005 socket to plug into the empty factory high beam plug on the passenger side of the car.
This would power my relay, making the relay switch ON when the high beams came on. Two wires from the headlight high beam to the coil inside the relay.
I then found the key wire. On my 99 C5 there is a wire that comes off and under the Micro Fog Light Relay #39 which is located in the fuse box next to the battery. It is a dark green wire with a white stripe that goes to the BCM …. This is the all-important grounding wire that the BCM turns off at the most inopportune time.
I “T’ed” off this wire and connected it to the switch able side of the relay and then to a good ground so that when the high beams came on, it would power my new relay and give the fog lights a ground that the BCM had just turned off.
I used no fuses with my new relay because it is powered by the factory high beam circuit, which already has a fuse.
So that’s it, fog lights now stay on when the high beams come on as well as the low beams, 6 lights. I could have put in a toggle switch in to turn off my new relay if I ever wanted the fog light not to come on with the high beams, but I’ll leave that for later if I ever need it. As it is now, when the high beams come on, I have no control, all 6 lights come on, which is fine, like I said, when I turn on my high beams I want light !!
Otherwise the fog lights work just like the factory setting.
Hope this helps.
03-10-2007, 12:49 AM
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Member Since: May 2006
Location: DuBois PA
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St. Jude Donor '11-'12-'13-'14-'15
Great write up, and very helpful!!! I'm planning on installing some neon or LED bars inside my side cove brake vents and this may be how I wire them up PLUS keep my fog lights on....
