An automobile fuse box diagram is a drawing that shows which devices are handled by a particular fuse, the amp rating of that fuse and its location in the fuse box. The diagram is in the owner's manual and can also usually be found inside the fuse box.
Fuses protect electric devices by preventing too much electric current, measured in amps, from travelling down the circuit. Automobile fuses, like fuses for home circuit boxes, are rated by the amount of current that they can carry before failing, typically ranging from 5 to 20 amps. Fuses are generally not difficult to change, so checking them can be one of the first things to do when a part of a car's electrical system stops working.
A fuse box diagram allows a vehicle's owner to locate a failed fuse and replace it with the proper fuse for that circuit. Fuse box layouts and a vehicle's electrical circuits are different depending on the manufacturer of the vehicle. Also, they tend to change over time, so diagrams are specific to the year, make and model of a vehicle. Many modern vehicles have multiple fuse boxes, so there may be more than one diagram in the owner's manual.