ordinarily the horn hooks to a relay which supplies power to the 1 terminal when the horn button puts a ground on the relay to activate it, and ground for the horn is the bolts that hold it. bolt the horn on and use any piece of wire [like a jumper cable] to quickly jump from the battery to either terminal of the horn to see what happens.
the way you've said it you may end up putting a dead short on yer battery the first time ya hit the button!
Bill
