relay for air horn

ok, well iv bought musical air horns and im readdy to fit em. the only thing is, the instructions are rubbish! i have a relay with 4 pins, now ive never used a relay before, ive tried to learn but reading is not as good a tool as using it and applying my knowledge,

so.... i need to know what size cables to wire from the relay to the compresser, and also where the other pins all go to!

I used 16-18gauge wires.

I initially wired it up, without the relay.  But blew a fuse for my brake lights. 

No more of that.

I'm just lost for the relay hook up itself.

I have a 5 connector relay using a 30amp.  

Posts are like this:

86

87

87a

30

Now, how would I wire this up so I dont blow anymore fuses.

Thanx in advance, and this is really the best informative site I've found. :)

Thanx Mitch for both reply's and PM  ;)