Fuses should be sized and located to protect the wire they are connected to. If a device like your car radio suddenly draws enough current to blow the fuse, the radio is probably already toast. The fuse is there to protect the wire, which would be much harder to replace than the radio. Most cars have two fuse panels. Another fuse panel, usually located in the dashboard, near the driver's knees, holds fuses for the devices and switches located in the passenger compartment.
Fuses are really just a special type of wire in a self-contained connector.
Most automotive fuses today have two blade connectors and a plastic housing that contains the conductor. There are also some fuses that are in the wiring of the car, called fusible links . An assortment of automotive fuses The conductor inside the fuse is made of a metal similar to solder. It has a lower melting point than the wire itself. The size of the conductor is calibrated very carefully so that when the rated current is reached, enough heat is generated to melt the conductor and so break the circuit.