Plugs and sockets wiring diagrams: 7 & 12 Pin Narva trailer plugs and sockets comply with all relevant ADR’s. “Small Round” and “Flat” connectors comply with Australian Standard AS4177.5-2004. “Large Round” and “Heavy Duty” connectors meet the new AS4735-2003 standard as required for vehicles and trailers over 3.5 tonnes. Available in either bulk or blister packaging, the range features plugs, sockets and adaptors in metal or ABS housings with nickel plated brass terminals.

*Cable entry view

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.