A relay is an electrically operated switch that allows current to flow through a circuit when activated. Relays are used to control high-power circuits with a low-power signal. In a car, relays are typically used for systems that require high current to operate, such as the headlights, fuel pumps, and air conditioning compressor. When a relay is energized, it closes its internal switch, allowing current to flow to the component it controls. Once the relay is de-energized, the switch opens, stopping the current flow.

    Relays are commonly used in situations where the current required to operate a device exceeds the capacity of a simple switch. For example, the headlights in a car require more power than a standard switch can handle. A relay allows a small amount of current from the car's electrical system to control a larger current that powers the headlights. This prevents the need for thick, bulky wires and allows the vehicle's electrical system to be more efficient and compact.