The electrical circuits of a vehicle are protected by fuses, circuit breakers, and fusible links. The main fuse/relay panel is in the engine compartment, while the interior fuse/relay panel is below the glove box. Each fuse protects a specific circuit, and the fuse panel identifies the circuits. There are different sizes of fuses, including small, medium, and large, all with the same blade terminal design. Medium and large fuses can be removed by hand, but small fuses require pliers or a fuse-puller tool. When an electrical component fails, check the fuse first. Use a test light to check for power at the exposed terminal tips of each fuse. If power is present on one side but not the other, the fuse is blown. It can also be visually inspected for signs of being blown. Replace blown fuses with the correct type, as fuses of different ratings may physically fit but should not be used. The amperage value of each fuse is molded into the top of the fuse body. If a replacement fuse immediately fails, isolate and correct the cause of the problem before replacing it again. Fusible links are used in circuits that are not typically fused, such as the alternator circuit. On some vehicles, the alternator circuit runs from the battery to the underhood fuse box and then to an inline 200 amp fusible link. Circuit breakers protect specific circuits like power windows and power seats. Depending on the vehicle's accessories, there may be multiple circuit breakers for door locks and power seats. Circuit breakers reset automatically, so if there is an electrical overload, the circuit will momentarily fail and then come back on. If the circuit does not come back on, it should be checked immediately. Use a voltmeter to test each end prong of the circuit breaker for battery voltage with the negative lead on a good chassis ground. If there is battery voltage only at one end, replace the circuit breaker.
