MIStateCJ

I have a 2016 Sierra 2500 that I am wiring in a Whelen Power Airhorn to. I have all the components wired, but in order to trigger the unit from the horn ring, it needs the positive horn wire to activate the unit. I was able to located the ground side in the Green BCM plug, it is the GN/WH wire. Does anybody know where this wire may be? I would prefer to tap in to it inside the cab without having to go through the firewall again and keep it cleaner. If I am reading the below correctly, there may not be a + inside the cab, but I wanted to verify. At the very least, see if there is a diagram out there that I have not found yet. Thank you! Battery positive voltage is applied at all times to the horn relay coil and the horn relay switch. Pressing either of the horn switches applies ground to the horn relay control circuit. The BCM may also apply ground to the horn relay control circuit as described above. When the horn relay control circuit is grounded, the horn relay is energized and battery positive voltage is applied to the horns through the horn control circuit. The horns sound as long as ground is applied to the horn relay control circuit