This is used on a 2015 Sierra.
I wanted to bring this thread back since I have seen others ask about low beams with fogs and I myself have been trying to figure it out. Yes the fogs with high beams is simple but since there in no “relay” command near the BCM for the low beams this was the best way I found out how to do it.
Have 2 wires grounded on the 30 and 85 terminals. These will go straight to ground somewhere in the general area of the BCM. The 86 trigger terminal will go to the body control connector X4 which is the black on either pin 1 or 2 wires. Both are yellow. These are the low beam supply voltage wires. The 87 terminal will go to the fog lamp relay wire on the brown connector pin 10. Fogs come on only with low and high beams. This way the parking lights by themselves come on without the fogs. This setup converts 12v positive to 12v ground which is needed o turn the fogs on. When you flip between low and high beam the fogs stay on.