Relays are electrical switches used to convert a small electrical load into a circuit capable of handling a high amperage load. Computers and small switches are not designed to carry the higher amperage requirement of a circuit that may have an electric motor, solenoid, or high amperage lighting fixture. Within a relay are contacts that are controlled with electromagnetism, when the circuit switch commands the device on or off, magnetism will pull or release the contact arm closing or opening the contacts within the relay that carry the voltage.