Stumpalump
Expedition Leader
Put a meter on your horns and have somebody press the button. You will see a voltage drop. If it's more than 1.3v then just add a relay near your horn to get the voltage back up. If that's not enough then snag old Cadillac horns out of a junkyard. You will already have the big relay to power them so you can just add them along with your stock horns.