A number of electrical items in the car such as the fuel injection,
Horns, starter and the fog lamps use relays to send electrical signals to the parts. The principle of operation of relays is that a small current, called the control circuit, is used to switch the current of a large current, called the power circuit. The faulty relay will lead to inappropriate functioning of the component in question. In most cases, the majority of the relays are mounted in the engine compartment fuse/relay box.