hahahahahhhh
instead of playing around in the dash, it might be easier to locate A) the positive wire going to one of the high beams and B) positive wire going ot the horn
and connect the two . you might possibly blow a headlight fuse, unless you disconnected the hi-beam's wires from them...dunno how much power the horn actually uses.
OR you could get one of those 140-db aftermarket horns and wire that straight to one of the hi-beams.