Automotive relays are for use in 12 volt electrical systems. Relays are used when you need to switch higher currents than a switch can handle, or when you want to isolate an electrical circuit. Our relays have either 5 contacts or 4 contacts. Relays with 5 contacts are called Changeover Relays, and are capable of switching between two separate output circuits - a normally open circuit and a normally closed circuit. Similar to a single pole single throw ON-ON switch, these relays can 'change over' from one circuit to another, and can be used to either turn a circuit on, or turn a circuit off. We carry relays for different amperage ratings. Our 30 amp relay is our most economical. It is a 5 terminal change over relay with a plastic housing and built in mounting tab. Our 40 amp relay is our most popular 5 pole relay and features a removable metal mounting tab. Our 50 amp relays also come in sealed versions with a resistor or diode across the relay coil. Our 60 amp relay offers the highest switching capacity in the standard Bosch 5 pin layout. Even higher power switching is available in our 4 pole 80 amp relay and 200 amp relay. We also carry a very popular pre-wired relay socket. The sockets can also be locked together if needed. For an overview of how a relay operates, please watch our instructional video.