You must have the correct vehicle wiring when using your trailer. Trailers not equipped with brakes will have a 4-way flat plug and all other trailers will have a larger 7-way plug. Don’t forget that a ground wire running from the plug back to the frame of the tow vehicle must be incorporated into proper tow vehicle wiring. Below are diagrams of the 4-way and the 7-way plugs.
White = Common Ground
Blue = Electric Brakes
Green = Tail License & Running Lights
Black = Battery charger , Hot, & Dome light
Red = Stop & left turn signal
Brown = Stop & Right turn signal
Yellow + Extra Auxiliary