As one should know, if the fuse pops the circuit is drawing more currrent or amps than the fuse can provide. When does the fuse blow? When you turn the headlights on, blow the horn, apply brakes, etc. If it blows right away after doing one of the above, you might have a short in the wiring to that device. You also might be asking for too much from that one fuse. Maybe hooking the horn on another fuse will solve your problem. Better yet, add a horn and headlight relay if you don't already have them. Horns are known to be amp hungry.
