Yes, high electical current (short) flowing through a wire that is sized too small for the amps its carrying will cause this. Our cars usually have good sized wires, so you are flowing a LOT of current to get the wire so hot it melts. You need to track down why so much current is flowing through these wires "before the fire" as someone else on this site has wisely said before. You could go through and check your fuses. Make sure a P.O. hasn't put tinfoil over a fuse or something dumb like that. It likely isn't a fused source doing it as the fuse would blow. Check other systems that don't go through the fuse block. You could unhook stuff one wire at a time at the horn relay bus and see if you can track it down.