I've also heard that if the horn itself is shorted out, it will just blow the fuses. Also, if this is on a 88, you might need to replace the foam in the horn button if it is honking by itself. The horn switch is two pieces of copper with foam in between. When you compress the foam, the horn honks. As the foam deteriorates, it will complete the circuit and honk by itself. I used some headliner foam about 1/8"-3/16" thick with holes cut out where the bumps are to replace my foam, others have found thin scotch brite pads or foam sponges that have worked. Just remove the horn pad and take it apart, it will be pretty obvious how to fix it. Just don't make it too thick or forget the cut outs, or it won't honk at all.
Good luck!