The horn in your car is great for getting your friend's attention as you pass him on the street, but really, not for much more than that. People pretty much ignore car horns these days. What you need is a horn that will get the attention of the drivers around you when you need it most. In other words, a loud horn. You need to install a relay, however, in order to supply the higher current needs of louder horns.
Locate and securely mount the horn and relay. This should be within 4 feet of the battery.
Strip 1/8-inch from the red 12-gauge wire by gripping the wire with the strippers and pulling the wire out. Insert the wire into a yellow spade lug and firmly crimp the connector by squeezing it with the crimper. Plug this into the plug labelled 87 on the relay.
Route the red wire to the positive terminal of the battery safely, avoiding pinch and scrape points. Cut the wire with wire cutters at the terminal, leaving slack for the wire to move. Strip 1/8 of an inch of wire and crimp a yellow butt splice to the wire. Connect the fuse holder to the other side of the butt splice and crimp securely. Insert and crimp a yellow ring terminal to the other end of the fuse holder and place it near the battery.
Crimp another yellow spade lug to the remaining red wire and connect this to number 30 on the relay. Route and connect the other end to the new horn's positive power input.
Strip 1/8 of an inch from the end of the 12-gauge black wire and crimp a yellow ring terminal on the end and secure it to solid ground. Route the other end to the negative input of the horn and connect it.
Strip a short piece of black wire and connect a yellow spade lug to it and connect this to number 86 on the relay. Route the other end to a solid ground and connect the wire to the ground. This is best accomplished by crimping a 1/4 ring terminal and bolting it to a solid ground.
Connect the red wire to the battery's positive terminal. Usually this means removing a nut on the battery's positive terminal and putting the ring terminal on the bolt and replacing the nut. Test your new horn
Twisting the strippers on the wire helps cut through the insulation better. If the horn sounds when you connect the red wire to the battery, you've connected the output to the wrong terminal. Move it from 87A to 87.