Wiring Tips: Using Relays | Offroaders The method I use for wiring the lights and other external accessories, for the most part, follows the diagram pictured above. As in the diagram a wire is run from a 12 volt power source to the switch in the cab and out to the relay placing a fuse at the source of the power. Free Wiring Diagrams - No Joke - FreeAutoMechanic Wiring Diagrams This is not an automated service. Each Diagram that is requested has to be hand selected and sent. As this is a free service it receives an overwhelming amount of requests and may take up to a week or longer for a response.