What would cause the high beam and fog light fuses burn out on 200 ford exlorer?

Answer 1

Fuses are installed in electrical circuits to protect the wires [conductors] in the circuit in which they are installed. When current [measured in Amps] flows through a conductor, some heat is generated. The greater the amount of current [higher the amps] flowing, the greater the amount of heat generated. There is a point where the heat generated can damage the insulation on the conductors, and even cause the metal [usually Copper] conductor itself to melt. This kind of heat can easily result in starting a fire in adjacent combustible materials. For this reason, fuses are installed in electrical circuits, with the intent that the fuse will melt open ["blow"] before the wire heats enough to damage its insulation. Any time a fuse blows, it means that more current was flowing through the conductor [wire] than it was capable of safely carrying. The most common cause of a fuse failure is that something has damaged the insulation on a "hot" wire, allowing it to come into contact with a ground. There are many scenarios, but one would be that due to viabration, the insulation of a wire passing over the sharp edge of body sheet metal, would chafe through, allowing the hot conductor wire to touch the body sheet metal which is grounded. That "short circuit"would allow tremendous current to flow, resulting in, hopefully, a very quick failure/blowout of the fuse, thus "turning off" the flow of current to the short, and protecting against further damage and the possibility of a fire. Another cause for excessive current flow is that someone who did not know what he was doing, added an excesssive extra load. A couple of examples of extra load include adding more, or larger, fog lights or headlights than the electrical circuit was designed to safely serve, or the addition of a several hundred watt sound amplifier to the circuit. Your described problem can be corrected by finding out what is causing the excessive current draw on the circuit, and the remove that cause. Then when the circuit has been corrected to be as it was designed and originally installed, the fuse(s) will not continue to blow.