A blown fuse indicates it has properly done its job, but it also means you have a job to do. Fuses are installed to protect electric components, or their respective power supplies, from shorts or power surges. Excessive amperage breaks the fuse, which then severs the flow of electricity. This prevents continued exposure to equipment damaging electricity. Fuses do not normally blow without a reason. If your fuse blows--especially if it happens repeatedly on the same fuse--it may be indicative of a larger problem, such as a short in the system.
Disconnect the device containing the fuse from the power supply. Most devices can simply be unplugged. If you are working on an automobile, disconnect one of the leads of the battery by loosening the nut on the lead connector and pulling it off.
2
Locate the fuse box or fuse holder. Consult your owner's manual if necessary. Automobile fuse boxes are typically under the hood or under the dash. Inline fuses--those that have fuses built into the cord--can be located by following the power cords and looking for a larger area labeled "fuse."
3
Open the fuse compartment if the fuse is not visible. This may require unscrewing a couple of screws, pulling down on a tab or pulling off a plastic cover. Your owner's manual should provide further instructions.
4
Pull the fuse out of the holder. Most fuse holders simply clip in place. Others may require you to loosen some screws. If you encounter resistance, use a fuse puller, which allows a better grip on the fuse.
5
Inspect the fuse to verify it is blown. For most fuses, this will be obvious. The fuse may appear blackened, or the visible filament will be severed. Some might require testing by touching the two leads of an ohmmeter to the two ends of the fuse. A zero reading means the fuse is good; an infinite reading means it is blown.
6
Compare the fuse with the replacement fuse to verify they have the same specifications. The amp rating should be marked on the fuse, and you should use the same rating for the replacement.
7
Install the replacement fuse into the holder, just as the previous one was installed, and close up the compartment.
8
Reconnect the device to the power supply and test the unit.
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