you hear the horn relay click which means the problem is either the wire going to the horn or the horn itself. mitsu's usually have the horn bolted to the chassis which acts as the ground, and one wire running from the underhood fuse/relay block to the horn itself supplying the 12volts.

you want an easy test....

take a wire and put it where the wire plugs into the horn, and take the other end of the wire and put it on the battery positive post.....if the horn blows, then the horn's not the problem, there's a loose connection or break in the wire coming off the relay going to the horn.