Here is the circuit Doc describes. The horn switch completes the circuit through the relay coil, magnetizing its core and closing heavy duty contacts that complete the circuit, sounding the horn.
20 Amp Fuse
1 Amp Fuse
This horn circuit is standard and almost any 12 volt vehicle with a horn relay uses this setup.
12 VOLT BATTERY
Drawn by Jon Pardue 8-15-2006