The white wire ground on the following boat trailer wiring diagram is drawn in grey so that you can see it against the white background. The four wires control the turn signals brake lights and taillights or running lights.

4e9827 Wesbar Tail Lamp Wiring Diagram Wiring Library
Boat trailer light wiring diagram. As the name implies they use four wires to carry out the vital lighting functions. We recommend these standards because they are pretty universal. 4 way trailer connectors are typically used on small trailers such as boat snowmobile utility and other trailers that that do not use brakes. Trailer wiring diagrams 4 way systems. On most recreational vehicles. 4 way trailer connectors are.
7 way trailer connectors are used by the following vehicle types. They also provide a wire for a ground connection. The following trailer wiring diagrams and explanations are a cross between an electrical schematic and wiring on a trailer. Large 5th wheel trailers. 4 way flat molded connectors allow basic hookup for three lighting functions. Right turn signal stop light green left turn signal stop light yellow taillight license side marker brown and a ground white.
7 pin trailer wiring diagram with brakes. The standard four prong connector to connect the trailer to the tow vehicle is perfect for a simple trailer light system. 7 way trailer wiring diagram is explained in details in the picture and the table below. That said for specific situations there are industrial standards with different connectors and wire arrangements. Notice the four prong connector on my boat trailer has 5 wires coming out the bottom.