Since many are throwing their two cents in, I thought I would contribute my penny's worth. If you draw a higher current through the circuit which was designed for x amps, you also run the risk of each and every connection/terminal (including grounds) degrading faster than if your circuit was operating as designed. Notwithstanding the fact you also may be STARVING (to what degree I have no idea, its food for thought though) necessary voltage/current levels for those components that are sensitive to such spikes and dips (and we all hear a lot about how our cars are electrical/electronic touchy). I would do as the instructions relayed (pun intended) and supported by those knowing and unknowing (but cautious) and wire in a controlling relay to the existing horn circuit (instead of the horns blowing, the relay acts as the load (horn) and which in turn drives the horns from a dedicated high current buss from under the hood).


Simply put, don't starve any circuit within or directly nearby the horn circuit to feed a high current device. Use a controlling relay and switch all available current closest to the source (battery) for those devices..