In the vehicle, the components that employ relay to switch the electrical signal involves the fuel injection system,
Horns, starter, and the fog lamps. A relay uses a low current circuit, called the control circuit to switch on and off the high current circuit referred to as the power circuit. This implies that a defective relay will lead to the improper functioning of the component related to it. Generally, relays are mounted, or at least their chassis-mounted terminals are accessible, in the engine compartment and interior fuse or relay boxes.