Though they do not sound important, car relay and fuses are crucially important. The automotive fuse and relays protect wiring and electrical components of a vehicle. Usually, they are rated less than 32 volts of direct current, however, some can reach up to 42 volts of current, which are of non-automotive use. These should be sized and designed in order to protect the wire they are connected to. To understand it better, take an example of your car radio, suddenly it ceases to draw enough current to blow the fuse, resulting in a toast of a radio. The fuse block is made to give protection to the wire. Most of the automotive come with two fuse panels. The first one is located in the engine compartment and hols the fuses for components like anti-lock brake pump, cooling fans and the engine control unit. While the other one is situated dashboard, which holds fuses for switches and its similar things in the passenger compartment. The fuse relay box car offers complete protection when the fuse blows.
The Relays, on the other hand, are self-contain cubes with wires going into it. These allow small control signals to run heavy equipment that uses large signals like starter, air-conditioning, headlamps etc.