An automotive relay is an electronically-operated switch, with electro-mechanically operated switches being the most common type used in the automotive industry. Automotive relays, as the name suggests, are specifically designed to carry out a multitude of high-current applications in vehicles, including cars, vans, trucks, trailers, boats and more. These applications can vary, from operating speakers, pumps, heaters and air conditioning, and motors, etc.
The most common automotive relays are 40A, but there are also 30A and 20A automotive relays - for applications requiring 10 Amps or lower, it is typical practice to use PCB-mounted relays. Automotive relays are typically available in 4-pin or 5-pin variations, but in both variations, two of these pins are connected to the internal coil to pass across the typical 12V required by most models of car. This 12V will then act on the internal switch in the relay.