The fuse box is often located in a cluster of components, as illustrated here. The box is shown with the cover off.
The starter motor has its own heavy cable, direct from the battery. The ignition circuit furnishes the high-tension impulses to the sparkplugs; and the charging system includes the generator, which recharges the battery. All the other circuits are called ancillary (subsidiary) circuits.
To guard against this, ancillary circuits have fuses. The most common type of fuse is a short length of thin wire enclosed in a heatproof casing often glass. The size of the fuse wire is the thinnest that can carry the normal current of the circuit without overheating, and it is rated in amps.
Apart from the main charging, starting and ignition circuits, there are other circuits that power lights, electric motors, the sensors and gauges of electrical instruments, heating elements, magnetically operated locks, the radio and so on. All Circuits are opened and closed either by switches or by relays - remote switches operated by electromagnets.