I installed an Air horn on my truck, at the same time I installed a compressor, solenoid valve, horn relay, and a push button switch. Currently it is not wired into my vehicle horn relay, and that is what I am now trying to do. I am trying to contain the wiring to the inside of my cab. I have put a multimeter on 3 different wires that I think go to the horn switch and I get no voltage. When I look for a schematic for the horn circuit all I find is for a 2003 Silverado, my truck is a 2007 Silverado, I would think that the schematic would be close. The question that I have is; Does the wire running from the factory horn relay going to the horn switch have 12 VDC power or is this a negative wire just providing a ground. My current wiring schematic for the air horn is set up as required for the Wolo Solenoid valve and I want to run a jumper wire from my horn switch wire to the back side of my air horn so that when I hit my regular horn the air horn goes off as well. In order to do this I need the 12 VDC to open the solenoid valve.