Yukon SLT Fog Lights Setting

CaptainMurray said:

Check BoostAutoParts.com, simple connection. $23

2007 - 2025 GM All Lights Mod (6 High Mod)

This kit allows your fog lights and low beams to remain on along with your high beams on GM truck & SUV's from 2007-2025. Installation takes less than 10 minutes while following our video. Mod is also known as the All Light On Mod or the 6-HI modification. Free shipping included, and MADE IN THE...

boostautoparts.com

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That doesn't exactly look like it's "plug and play," but at least it's something.

Now, does it keep the fogs on from the last time you turned them on? (Does it allow "auto-on" fogs when the headlights come on?) Tough to tell from the description.

KMeloney said:

That doesn't exactly look like it's "plug and play," but at least it's something.

Now, does it keep the fogs on from the last time you turned them on? (Does it allow "auto-on" fogs when the headlights come on?) Tough to tell from the description.

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On the web site, says not compatible wtih 2021, 2, 3, or 4.

If you check the upfitter site, you will find that the fogs On/Off is controled by the BCM (Body Control Module) signaling the LCM (Lighting Control Module), and the details imply the signaling from the LCM to the actual lamps is a PWM (pulse width modulated) signal (presumably to contol the brightness), not a constant 12V (It may not even be 12V, it could be 5V or less, since the fogs are LED.

Worse yet it appears the signal from the BCM is serial as well...so, it isn't real straight forward to pull this off.

See lighting section of this document, starting at pg 2-13. Esp the Description of Operations section.

WalleyeMikeIII said:

On the web site, says not compatible wtih 2021, 2, 3, or 4.

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And yet in the link description above, it says it is.

Thanks for confirming what I believed to be true in the first place!

KMeloney said:

That doesn't exactly look like it's "plug and play," but at least it's something.

Now, does it keep the fogs on from the last time you turned them on? (Does it allow "auto-on" fogs when the headlights come on?) Tough to tell from the description.

Click to expand...

they have a variety of different ones, I didn't read over all of them but it looks like they do have a option like that.

WalleyeMikeIII said:

On the web site, says not compatible wtih 2021, 2, 3, or 4.

If you check the upfitter site, you will find that the fogs On/Off is controled by the BCM (Body Control Module) signaling the LCM (Lighting Control Module), and the details imply the signaling from the LCM to the actual lamps is a PWM (pulse width modulated) signal (presumably to contol the brightness), not a constant 12V (It may not even be 12V, it could be 5V or less, since the fogs are LED.

Worse yet it appears the signal from the BCM is serial as well...so, it isn't real straight forward to pull this off.

See lighting section of this document, starting at pg 2-13. Esp the Description of Operations section.

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you should be able to bypass all that nonsense with a simple relay, 12v to the light, triggered by whatever you please

Doubeleive said:

they have a variety of different ones, I didn't read over all of them but it looks like they do have a option like that.

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You read the post that says they do NOT have one for the '21-'24 Yukons, right?

Doubeleive said:

you should be able to bypass all that nonsense with a simple relay, 12v to the light, triggered by whatever you please

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I don't think the light takes straight 12V, It takes a Pulse Width Modulated input of some sort (to the LED's). From the Schematic below, see red circled indicators. Common w/ LED's to control brightness and improve longevity.

KMeloney said:

You read the post that says they do NOT have one for the '21-'24 Yukons, right?

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supposedly, not sure what the differences are between the 2024 silverado and a 2024 tahoe. I would gamble it could be made to work (maybe) someone would have to call and ask them, could simply be bcm wires are in a different location

WalleyeMikeIII said:

I don't think the light takes straight 12V, It takes a Pulse Width Modulated input of some sort (to the LED's). From the Schematic below, see red circled indicators. Common w/ LED's to control brightness and improve longevity.

View attachment 440510

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all you have to turn on is the trigger then, this cannot possibly be that complicated. even if you have to connect right behind the fog light button.

Doubeleive said:

all you have to turn on is the trigger then, this cannot possibly be that complicated. even if you have to connect right behind the fog light button.

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I don't think you can do it automatically as the OP requested (so the fogs just come on whenever the headlights are called for being on by the BCM). Since the BCM just takes the input from the Ambient Light sensor and commands the Lighting Control Module to turn on the Headlights (via serial command, I think), there isn't an obvious way to do it that I can discern from the limited info at the Upfitter site.
From Pg 2-42


And here is the description of turning on the headlamps manually.



Note, I found nowhere in the upfitter manual that describes the "Fog Light" operation, but looking at the schematics of the fog lamp section, it indicates fog lamp switch (which is part of the headlamp switch, S30) is connected to pin 7 and Pin 18 of the BCM, and the Fog Light Switch and the Instrument Panel Dimmers (both of which are normally open, momentary contact switches), serve to short out various portions of a resistor divider network, thereby creating four different voltages which can bee seen on pin 7 of the BCM. Each voltage presumably serving to actuate a different response by the BCM; One of which I presume is a serial command to the LCM to turn on the fog lamps. Here is that schematic:


Perhaps one could wire a circuit in parallel to pins 11 and 12 on the headlamp switch that provides a momentary equivalent resistance across those pins to tell the BCM to actuate the fogs (simulating a fog light switch press), but then you still have to contend with where to get the signal to fire this circuit in the first place. For the manual headlamps on case, it is pretty easy, you take the ground out of the headlamp switch. For the full automatic control the OP desired, you would have to decode either the Ambient Light Sensor voltage, or the serial command from the BCM to the LCM to turn on the head lamps.

Hey, I have been wrong before, so, I may be missing something obvious...feel free to suggest any way you see to make it happen.