Relay Wiring Diagram
A relay is typically used to control a component that draws high amperage. The relay allows full power to the component without needing a switch that can carry the amps. The switch only controls the relay. The relay then provides a direct connection to the battery. It should be noted that either the power(86) or ground(85) in the relay control circuit can be switched. In the case of a horn, the horn button would be used to switch the ground lead(85) and power(86) would be provided directly from the fuse box.
This is a typical wiring diagram for
a standard relay installed for
headlights, horn, fuel pump, electric fan, etc. If the relay has a
5th terminal, it is not used.