Trailers towed behind a vehicle can obscure the rear lights of the towing vehicle, so in most areas they are required to have their own lights, linked to the vehicle's wiring. A connector plug electrically links the trailer into an outlet attached to the car. The plugs are available with between four and seven connections, four being the most basic legal requirement. Wiring the connector requires attention to detail, good color vision and the ability to use basic tools.
Locate the four-way connector at the rear of the towing vehicle. If it is a flat block, it will be a polarized connector with three female connectors molded together in an insulated block and one exposed male connector. The connector may also be circular and consist of four female connectors arranged in a square formation. Confirm that your tow vehicle connector is attached to four wires: green, yellow, brown and white. If it is not, you will first need to wire the vehicle connector before attaching a trailer.
Disassemble the connector that came with the trailer wiring system. With the housing removed, offer the connector up to the vehicle connector and hold it in the right position to connect it to the tow vehicle. Observe where each pin would connect to the vehicle. Record the color of the wire corresponding to each pin.
Strip the outer insulation from the last two inches of the trailer wiring cord to expose the four wires within it. Lay the cord in the connector housing, with the last insulated part aligned with the cord grip. Route each wire to the correct terminal, matching identical colors, and cut them to the required lengths.
Strip the insulation from the last 1/4 inch on each wire. Connect the wires to the appropriate connector terminals. If you do not have a tow vehicle connector to copy, wire a round connector as follows: When looking at the front side of the 4-way round plug, the top left pin is for the green wire and the top right is for the yellow wire. Brown and white go to the bottom left and right, respectively.
Secure the cord in the cord grip, reassemble the connector housing and plug it into the tow vehicle outlet. Test the wiring by activating the brakes, tail lights and both turn signals. If any of the lights fail to operate, or the wrong light activates, check the connections as follows: Green wire for the right turn and right brake light; yellow wire for the left turn and left brake light; brown for both tail lights. White is the grounding wire, so if none of the lights work, check this connection.
