Wiring Fog Lights

Cherokeekid88

Cherokeekid88

Well-Known Member
Joined
Jun 30, 2007
Location
High Point, NC
Was talking to my brother yesterday and he had wired some small led lights (Those little orange lights you see in the grills of yota's) on his FJ and wired them up to his fuse that goes to his headlights using a fuse splitter? Him and I are going to tackle installing fog lights on my 17 KL next weekend and am wonder if you could wire LED foglights this same way or is that too much power? I am a complete noob when it comes to electrical stuff, so just wondering. I didn't really want to add a switch anywhere in the car and have read that it can't be spliced into the existing wiring harness for the headlights. So just trying to explore my options.
 
Proper way would be to add a relay that uses the same switch/signal 12v source as the headlight relay. Should be able to use a fuse tap to get the signal for the relay. There's definitely janky ways to do it that will work but ain't no sense in doing janky stuff on something that ain't a shitbox.
 
Chris_Keziah said:
Proper way would be to add a relay that uses the same switch/signal 12v source as the headlight relay. Should be able to use a fuse tap to get the signal for the relay. There's definitely janky ways to do it that will work but ain't no sense in doing janky stuff on something that ain't a shitbox.
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I agree. Part of the reason why I don't want to drill into the dash to add a switch somewhere. I really just want to be able to use my headlight switch and them come on every time I turn my headlights on.
 
Is the headlight switch an actual headlight switch, or just an input on the canbus that tells the ECM to activate the headlights? That will inform where it would be best to tap your relay. If you tap directly off the power wires going to the headlights, that will avoid some of the uncertainty, and keep all the wiring under the hood.

Don't connect the new lamps themselves directly to the existing headlight circuits. The relay draw is minimal (likely ~200mA or something like that).
 
shawn said:
Is the headlight switch an actual headlight switch, or just an input on the canbus that tells the ECM to activate the headlights? That will inform where it would be best to tap your relay. If you tap directly off the power wires going to the headlights, that will avoid some of the uncertainty, and keep all the wiring under the hood.

Don't connect the new lamps themselves directly to the existing headlight circuits. The relay draw is minimal (likely ~200mA or something like that).
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I have an actual dial that turns the running lights and headlights on, but not sure on the canbus part of the question. I do know that when I tried to add LED License plate bulbs, it would throw a message to my dash telling me they are out...I'm guessing because of the draw of power is nowhere near a halogen bulb with LED.
 
Cherokeekid88 said:
I have an actual dial that turns the running lights and headlights on, but not sure on the canbus part of the question. I do know that when I tried to add LED License plate bulbs, it would throw a message to my dash telling me they are out...I'm guessing because of the draw of power is nowhere near a halogen bulb with LED.
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Pretty much everything you need to know in that sentence. If you've got a module that does current monitoring of the power circuits, this is very different than a traditional switches-and-relays power setup from the olden days. The dial is completely CAN-based most likely.

If you have HID headlights, you may or may not be able to tap off of the headlight power for a relay trigger, depending on how the power is configured. Many HID ballast units are a multi-wire instead of just power and ground, so some of the traditional power control is sometimes built into the ballast unit. But, if needed you can easily tap off a marker light or some other light that turns on with the headlights in order to trigger a relay coil for the fog lights. Really any 12V output that is controlled when the headlights are turned on will work.
If current draw from the relay coil is an issue at all, a mini relay (they have a higher coil resistance so lower coil activation current) or a solid state relay would be the solution.

I'd take a look at the fog lights and see if they already include anything that you need, before actually buying anything.
 
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And make sure they only trigger with your low beams...
 
Fabrik8 said:
Pretty much everything you need to know in that sentence. If you've got a module that does current monitoring of the power circuits, this is very different than a traditional switches-and-relays power setup from the olden days. The dial is completely CAN-based most likely.

If you have HID headlights, you may or may not be able to tap off of the headlight power for a relay trigger, depending on how the power is configured. Many HID ballast units are a multi-wire instead of just power and ground, so some of the traditional power control is sometimes built into the ballast unit. But, if needed you can easily tap off a marker light or some other light that turns on with the headlights in order to trigger a relay coil for the fog lights. Really any 12V output that is controlled when the headlights are turned on will work.
If current draw from the relay coil is an issue at all, a mini relay (they have a higher coil resistance so lower coil activation current) or a solid state relay would be the solution.

I'd take a look at the fog lights and see if they already include anything that you need, before actually buying anything.
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Might as well had been typing in Russian.... : )

The fog lights I have, have a male and female 9006 connector and then about 6 inches of wiring coming off of that. (Power and ground)

Head lights are HID, DRL are LED. I have everything to install the fogs, just haven't bought anything as far as wiring because A.) I have no idea what I am doing and B.) Not sure of my options, so didn't want to spend money on anything till I know what I can actually do.

Ron said:
And make sure they only trigger with your low beams...
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Yes, Exactly.
 
Cherokeekid88 said:
Might as well had been typing in Russian.... : )

The fog lights I have, have a male and female 9006 connector and then about 6 inches of wiring coming off of that. (Power and ground)

Head lights are HID, DRL are LED. I have everything to install the fogs, just haven't bought anything as far as wiring because A.) I have no idea what I am doing and B.) Not sure of my options, so didn't want to spend money on anything till I know what I can actually do.
Click to expand...

Are there any factory fog light connections at all? For example, could you just buy an OEM foglight kit from the dealer and install it? If that option is available, that means everything is there to tap off of, and that's probably the easiest location to tap off with the LED fog lights. Else you're going to need schematics for the HID system, so you can see if the headlight power is relay controlled, and how the high/low beam control works on the HID ballasts. Turning the fog lights on with the headlights is easy, but turning them off when the high beams are enabled may be considerably more difficult.

What vehicle are we actually talking about here?
 
Fabrik8 said:
Are there any factory fog light connections at all? For example, could you just buy an OEM foglight kit from the dealer and install it? If that option is available, that means everything is there to tap off of, and that's probably the easiest location to tap off with the LED fog lights. Else you're going to need schematics for the HID system, so you can see if the headlight power is relay controlled, and how the high/low beam control works on the HID ballasts. Turning the fog lights on with the headlights is easy, but turning them off when the high beams are enabled may be considerably more difficult.

What vehicle are we actually talking about here?
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2017 Jeep Cherokee.

So the brackets for the fog lights are there. The Bezel is not. Had to get some OEM fog light bezels as they just have an insert in its place right now. From what I have read, they use 2 different wiring harnesses (one with fogs, one without) The connector that you have to pull in order to get the front fascia off only has 3 wires total going to it. I've had all this stuff lying around for a while and I just want them installed already.

shawn said:
Sell it and buy one with the factory fog light option.
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Might be easier huh? lol
 
I found something about doing that on a Compass. Sounds like the fog light output needs to be enabled in the ECM or BCM or whatever, so even with the factory harness and lights you would need to have that done. So you're back to finding out more info about the HID headlights, and whether you could tap off of them for a relay enable.
 
Fabrik8 said:
I found something about doing that on a Compass. Sounds like the fog light output needs to be enabled in the ECM or BCM or whatever, so even with the factory harness and lights you would need to have that done. So you're back to finding out more info about the HID headlights, and whether you could tap off of them for a relay enable.
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Seems like I read something like that too about the ECM needing a flash, but thought it was because they used an OEM switch that had the fog light option and a OEM harness.


Guess my options right now are finding out if I can tap into the headlight harness or just doing by a switch inside on the dash....
 
Cherokeekid88 said:
Seems like I read something like that too about the ECM needing a flash, but thought it was because they used an OEM switch that had the fog light option and a OEM harness.


Guess my options right now are finding out if I can tap into the headlight harness or just doing by a switch inside on the dash....
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Yes, I was just mentioning that because that means it's not as simple as tapping off of any factory fog light wiring. I think the headlight harness is the best bet, if you can get enough information to find out if that's possible. Again, that could be difficult if the high and low beams are both in the same integrated headlight unit for each side.
 
I just got a chance to take a quick look at a pair of schematics I found earlier for the Grand Cherokee, one for the 2014 and one for the 2019. They're close enough in the areas that count. If the standard Cherokee is at all similar to the Grand Cherokee (they will be, if they're smart...), then this should be a simple install if you can verify wire colors and connectors, etc., for the Cherokee with a Haynes manual or whatever.

They're from here: WK2Jeeps.com - 2011-2020 Jeep Grand Cherokee menu page

Here's the gist of things:
  • There appears to be an enable from the ignition for each headlight module (left and right). That is probably where the control board power to each headlight module comes from.
  • The BCM controls a relay and fuse in the PDC (power distribution center) toward each headlight module that says "HID Lamp Driver".
    • That is probably the to turn the HID low beams on
    • Not sure if that toggles with the HID, so does power come on with the headlights, and go off with the high beams (that's the likely conclusion)?
    • It's likely the power though, because then the BCM could monitor the current draw of the lamp.
    • It will turn on/off with the HID lights, and will turn off when the HID lights shut off when the high beams turn on
  • The BCM has another output (no separate relay or fuse) labeled "High Beam Driver".
    • That is probably power for high beams, because of the word "driver".
    • It may be an enable signal instead of power, dunno.
    • It's likely the power though, because then the BCM could monitor the current draw of the lamp.
So if things are working like I think they would, you have a toggled power output for the HID low beam, and a toggled output for the high beam. That gives you everything you need for the fog lights.

So, now that I've spent a few minutes dissecting the functions:
  • If the "HID Lamp Driver" power is only on when the HID low beams are on
    • You only need a single relay.
    • Works the same way as it would with an old school headlight switch, but taps between the PDC and the headlight module, or between the BCM and the PDC (either would work most likely)
  • If the "HID Lamp Driver" power stays on continuously (I don't think that is what happens)
    • You will need a relay to turn on the fog lights with the HID lights
    • ....and another relay to turn them off when the high beams are enabled
  • You can figure out what's happening by probing the HID power with a voltmeter, while changing the headlight mode on the headlight switch

Other cool geeky shit that I saw: The Right-side module has a lot more stuff in it, and it communicates with the Left module over LINBUS, and to the chassis with CANBUS.

Because of that, it's probably a good idea to tap off of the wiring on the Left module, because it's much simpler than the Right side module. The Left has about half the wires as the Right, and the functions that you care about are the same on both sides..
 
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Fabrik8 said:
I just got a chance to take a quick look at a pair of schematics I found earlier for the Grand Cherokee, one for the 2014 and one for the 2019. They're close enough in the areas that count. If the standard Cherokee is at all similar to the Grand Cherokee (they will be, if they're smart...), then this should be a simple install if you can verify wire colors and connectors, etc., for the Cherokee with a Haynes manual or whatever.

They're from here: WK2Jeeps.com - 2011-2020 Jeep Grand Cherokee menu page

Here's the gist of things:
  • There appears to be an enable from the ignition for each headlight module (left and right). That is probably where the control board power to each headlight module comes from.
  • The BCM controls a relay and fuse in the PDC (power distribution center) toward each headlight module that says "HID Lamp Driver".
    • That is probably the to turn the HID low beams on
    • Not sure if that toggles with the HID, so does power come on with the headlights, and go off with the high beams (that's the likely conclusion)?
    • It's likely the power though, because then the BCM could monitor the current draw of the lamp.
    • It will turn on/off with the HID lights, and will turn off when the HID lights shut off when the high beams turn on
  • The BCM has another output (no separate relay or fuse) labeled "High Beam Driver".
    • That is probably power for high beams, because of the word "driver".
    • It may be an enable signal instead of power, dunno.
    • It's likely the power though, because then the BCM could monitor the current draw of the lamp.
So if things are working like I think they would, you have a toggled power output for the HID low beam, and a toggled output for the high beam. That gives you everything you need for the fog lights.

So, now that I've spent a few minutes dissecting the functions:
  • If the "HID Lamp Driver" power is only on when the HID low beams are on
    • You only need a single relay.
    • Works the same way as it would with an old school headlight switch, but taps between the PDC and the headlight module, or between the BCM and the PDC (either would work most likely)
  • If the "HID Lamp Driver" power stays on continuously (I don't think that is what happens)
    • You will need a relay to turn on the fog lights with the HID lights
    • ....and another relay to turn them off when the high beams are enabled
  • You can figure out what's happening by probing the HID power with a voltmeter, while changing the headlight mode on the headlight switch

Other cool geeky shit that I saw: The Right-side module has a lot more stuff in it, and it communicates with the Left module over LINBUS, and to the chassis with CANBUS.

Because of that, it's probably a good idea to tap off of the wiring on the Left module, because it's much simpler than the Right side module. The Left has about half the wires as the Right, and the functions that you care about are the same on both sides..
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Wow. thanks for all that info! So with all that being said, what time did you want to stop by? : )
 
Got the fog lights installed last week. (was a bit of a pain) Now, I just need to get them wired up. Still trying to find info on headlights and if I can tap into them. Might just end up adding a switch and doing it the old fashion way....Just would rather have a setup where they will go off when the car is off, just don't know if that's doable at this point.
 
Cherokeekid88 said:
Got the fog lights installed last week. (was a bit of a pain) Now, I just need to get them wired up. Still trying to find info on headlights and if I can tap into them. Might just end up adding a switch and doing it the old fashion way....Just would rather have a setup where they will go off when the car is off, just don't know if that's doable at this point.
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It seems do-able. It sounds like the best path is to find a local friend who is comfortable with a voltmeter to verify what I suggested above. Is there a Chilton or Haynes available for that model? That's all you really need, just something with schematics in it (wire colors would be stellar as well), at least to see if it's any different than what I've already figured out.
Or this, which must be new since last time I looked at Alldata: ALLDATAdiy.com: Factory-Direct Repair Information for DIYers and Students - ALLDATA
 
Yeah, I think I am going to try and find a local shop that's reputable and isn't going to just jimmy rig the wiring and let them have a go at it. I myself am just not comfortable enough to try and tackle it myself and want to make sure its done right. I just don't know anyone personally who is good with electrical stuff.
 
Got up with LED Designs outta Greensboro who had been recommended to me by several people. Called them up and they didn't seem to interested in tackling it since I wasn't purchasing fog lights from them, so now I am back to square one.
 
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