Many of the horn upgrades are horns that use more power than stock, requiring wiring a relay to avoid burning out your switch.
Saw this on the Feeger forum, a new horn by PIAA that uses the same power as most stock horns. Bolts on the same and uses the same blade connections. Plug and play. You can leave one stock horn and use only one of these:
http://www.compacc.com/p/PIAA-Slimline-Sports-Horn/1603005
I would guess you could use two also. I think this is a 2 horn kit:
http://www.amazon.com/85114-400Hz-5..._2?s=automotive&ie=UTF8&qid=1322849680&sr=1-2
Saw this on the Feeger forum, a new horn by PIAA that uses the same power as most stock horns. Bolts on the same and uses the same blade connections. Plug and play. You can leave one stock horn and use only one of these:
http://www.compacc.com/p/PIAA-Slimline-Sports-Horn/1603005
I would guess you could use two also. I think this is a 2 horn kit:
http://www.amazon.com/85114-400Hz-5..._2?s=automotive&ie=UTF8&qid=1322849680&sr=1-2