EASY TO INSTALL. No cutting! No splicing! This trailer wiring harness plugs into existing factory wiring on your vehicle and equips it with a standard 4-pin trailer wiring connector for plugging in and towing a trailer. STANDARD CONNECTOR. The 4-flat trailer wiring can be used to connect trailer taillights, brake lights and turn signals. 4-way trailer wiring is popular on a wide variety of trailers, adding versatile towing options for your vehicle. VEHICLE-SPECIFIC. This vehicle-trailer wiring harness is designed for select models of the Ford Focus, ensuring the easiest possible installation and the most reliable wiring connection.