4 Wire Trailer Harness | etrailer Wire your trailer with this universal, splice-in wiring harness so that you can connect the trailer's wiring to your vehicle's during towing. Wishbone design removes need for a jumper wire Features: 4-Pole flat trailer-end connector plugs into the 4-way flat on your tow vehicle 2 Tail light wires of wishbone-style harness make wiring your trailer more efficient One tail light wire Amazon: 4 wire trailer harness ROSI 6ft 4 Wire 4-Flat Trailer Light Wiring Harness Kit 4 Way Trailer Wire Extension & Wishbone-Style with 20 Gauge White Ground Wire SAE J1128 Rated，with 4 Flat Connector for Under 80" Wide Trailers. $11 $ 11. 49. Get it as soon as Mon, Apr 29. FREE Shipping on orders over $25 shipped by Amazon.