Originally Posted by Kenstaroni

I used the power wires that came with the supplied harness to the battery, then added another 12v wire separate and ran it back to the spot on the harness on the passenger side (for the switch). This extra wire came off my blue sea fuse box and is 12v constant.

The harness they include can make things confusing but study the wiring diagram and it will be pretty simple. Switch is not lit when off, and lit when on the way I did mine. You can wire secondary illumination where the switch is lit when compressor is off as well I believe, if so you would want this on a 12v IG source so it's not on all the time. My switch is in the engine bay, no need for it to be lit up when off for me.