What is the function of relays in automotive electrical systems?

Relays are electromagnetic switches that allow a low-current control circuit to switch high-current loads. When current flows through the relay coil, it creates a magnetic field that moves the contacts closed. Relays protect switches and ECUs from high current, enable remote switching of loads, and provide electrical isolation between control and load circuits. Common automotive relays include: Starter relay, fuel pump relay, horn relay, headlight relay, and cooling fan relay.