Yukon SLT Fog Lights Setting

[Doubeleive]

It seems doable...but 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). You could do it whenever you manually turn on the Headlights by also grounding out the fog lamp switch, I think). But, where 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
View attachment 440521

In the Manual Case of flipping the headlight control switch to ON, I think one could short the headlight ON signal that is stated to be grounded to the fog lamp ON signal and achieve the fogs on w/ the headlamps, but this only works when flipping the headlight switch manually...I still see no way to imitate the automatic version above. At least not without some serious analysis of the Serial Messaging from the BCM to the LCM. But hey, I have been wrong before.
View attachment 440522

depends on the vehicle and lighting type, but "typically" drl's run on less than 12v, more like 10v probably, then when the ambient light sensor commands the lights on you will hear the relay click (in the engine bay fuse box) and then the full 12v's is applied. a separate relay could connected to that trigger to power on the fogs at the same time.
It's just a matter of looking at the wiring and connecting a to b, (power and ground + trigger)
depending on how it is done you could maybe end up with a error on the dic, the fog light switch may no longer turn them off if so desired, no fog light indicator lit up in the cluster etc, etc.
I would look and see if there is a specific fog light relay or if they are on a separate circuit. if they are on a relay then you should be able to just patch the headlight trigger to the fog light trigger and then test if the fog light button still turns them off
**then you have to consider the "on with wipers" also, if the trigger is set to work with the headlights then they should just come on with the headlights and go out with the headlights

 

[WalleyeMikeIII]

depends on the vehicle and lighting type, but "typically" drl's run on less than 12v, more like 10v probably, then when the ambient light sensor commands the lights on you will hear the relay click (in the engine bay fuse box) and then the full 12v's is applied. a separate relay could connected to that trigger to power on the fogs at the same time.
It's just a matter of looking at the wiring and connecting a to b, (power and ground + trigger)
depending on how it is done you could maybe end up with a error on the dic, the fog light switch may no longer turn them off if so desired, no fog light indicator lit up in the cluster etc, etc.
I would look and see if there is a specific fog light relay or if they are on a separate circuit. if they are on a relay then you should be able to just patch the headlight trigger to the fog light trigger and then test if the fog light button still turns them off
**then you have to consider the "on with wipers" also, if the trigger is set to work with the headlights then they should just come on with the headlights and go out with the headlights

There IS no relay for the fog lights...its a PCM from the LCM...Low current, because LED...

 

[Doubeleive]

There IS no relay for the fog lights...its a PCM from the LCM...Low current, because LED...

meh, looking at a 2021 fog light online it has 2 pin's it's going to come on with 12v applied
if in doubt pull the connector off, turn the fogs lights on and use a meter on the 2 pins to verify the voltage

 

[Doubeleive]

once voltage is confirmed it's as simple as running a power wire from the headlight circuit to the fog light, if the only goal is to have fogs with headlights
only thing i would check is if the ground or power is cut when high beams are turned on and then connect as needed

 

[Doubeleive]

you could just buy a couple fog light harness and unplug the factory harness and wire as desired, then if for some strange reason some kind of factory warranty issue needed to be done with the lights you just plug the factory harness back in. there just lights....... I have been rewiring mine for 30+ years

 

[WalleyeMikeIII]

once voltage is confirmed it's as simple as running a power wire from the headlight circuit to the fog light, if the only goal is to have fogs with headlights
only thing i would check is if the ground or power is cut when high beams are turned on and then connect as needed

Not that simple…check the headlight wiring, 3 PWM inputs to the headlight assembly from the LCM, plus a separate high current power is direct from the fuse panel. Logic built into headlight assembly. Suggest a full review of the lighting section, these are not the old school headlights where switch controls actuate one of 3 relays to give the low/high/marker lamps, each a high current supply for their individual circuits.