Sounds like the wire for the headlights is shorted out somewhere. So the fuse is doing what is should, blowing to prevent a the wire from melting or starting a fire. Start at the headlights and look for any obvious damage to the wires. Look for pinch points or spots where it goes through a hole in the sheet metal. Any missing grommets? The wire may have rubbed a bare spot. If you can find the damage, repair it and fix whatever caused it. If you don't find it, take it to a qualified mechanic - don't bypass the fuse or put heavier fuses than the circuit is rated for in the slot. If you burn up the switch or wiring, you will have a much more expensive fix in the long run. Answer 1 is not incorrect, BUT when the headlight switch is turned on, it supplies current TO MORE THAN the headlights. It also feeds to the instrument panel lamps, front parking lamps, all side marker lamps, tail lamps, and to the license plate lamp[s]. Therefore, a SHORT in any one of the wires in ANY OF THESE circuits would cause the fuse to fail [blow out]. I don't know about the horn because I thought it was on a different fuse[circuit]. Also, as stated in answer 1, DO NOT bypass the fuse, DO NOT "OVERFUSE" the circuit, and take your vehicle to a QUALIFIED automotive mechanic, or better, an automotive electrical technician. j3h.