I want to get this small air horn from my work, it comes with to horn things and a small compresor. It comes with a relay, but I just want to take out my old horns and put the power wire on the + and ground the other side, will that work fine or do I have to hook up the relay? Me and my buddy hooked it up with some alligator clamps to a battery and it worked fine.

As far as a switch, you can use your factory horn button if you just disconnect your factory horns and run a wire from that connector to the relay.