Trailer connectors are wire harnesses designed to plug into the receptacle plug on vehicles designed to tow. While the receptacle plug is pre-wired to your vehicle, you will need to know how to wire a 5-pin flat trailer connector to have the trailer lights work. The process takes about an hour. All the wiring on any 5-pin flat trailer connector follows an industry standard.
Strip ¼-inch insulation off your #12 electrical wire using your electrical pliers and splice the end onto one of the lights on your flat trailer. Twist the bare wire of the wire from your light onto the wire you are adding and wrap it in electrical tape. Run the #12 wire up to the end of your trailer hitch so it can be spliced onto the wires of the 5-pin trailer connector. The trailer connector will then be able to plug into the receptacle on your vehicle.
Run the #12 wire up to the end of your trailer hitch so it can reach where it will need to be spliced onto the wires of the 5-pin trailer connector. The trailer connector will then be able to plug into the receptacle on your vehicle.
Cut the wire at the length you need and strip ¼-inch insulation from the end. Splice this to the corresponding wire from the 5-pin connector that matches the light you just ran the wire from. The wires from the trailer connector are color coded. Yellow is for the left side brake and turn signal, green is for the right brake and turn signal; and yellow is for the lights on your license plate. Connect each light to the 5-pin flat trailer connector. When you are finished, you will have two wires left over on the pin, white and blue, that are not connected to anything.
Splice the blue wire to whatever additional accessories you have on your flat trailer. This could be for additional side marker lights or any other running lights you have attached to the flat trailer.
Locate a bolt near the 5-pin connector that is set directly into the metal frame of the flat trailer. Remove the bolt. Strip the ends of a piece of #12 wire and crimp on a ring terminal large enough for the bolt to pass through. Splice the other end of the #12 wire onto the white wire from the 5-pin connector. Pass the bolt through the ring terminal and tighten the bolt back into the frame. This is the ground for your trailer connector.
