Relays are for sissys, nothing like a hot wire to keep the cab of your truck warm when the heater doesn't work. I would imagine that it is a low voltage switch but it should have a relay already there from the old A/C compressor. What would be really sweet is if what you are planning on using it for is under the hood then the wire that used to trigger the clutch could be used and it already has the old fuse right in the fuse block.
