http://www.classictruckshop.com/clubs/earlyburbs/projects/bosch/foglite.jpg
Here's a good basic relay diagram.
It doesn't matter what the accesory is, it's all the same. Most relays have two output terminals...you don't have to use both.
Also, since you will probably want use your regular horn button, you can go about wiring it several ways.
1)Air horn only...just cut the original horn wire and route it to the relay trigger pole.
2)Air horn and stock horn at the same time...pull a jumper from the horn wire to the relay.
3)Both but seperately selectable using the factory horn button...cut the horn wire and route it to an ON-OFF-ON toggle switch. Run one side to the regular horn, the other to the relay, then you can chose which horn you want to use.
I will say this...I have a similar horn in my truck and am very dissapointed with it. I have it wired like #2 and it sounds stupid when it goes off because it takes the compressor a split second to spin up. So when I hit the horn button, the stock horns go, then the air horn goes just after...it just sounds goofy.
I will soon be removing that horn for a set of real air horns with a small electric compressor...I just need to get myself motivated to do it.
