5 Wire Trailer Harness | etrailer This wishbone-style, 5-wire flat harness is great for a trailer with a surge coupler. The 40' long harness includes a 4' long ground wire and a blue auxiliary wire that signals your trailer Features: 5-Way flat connector provides a male plug for your trailer Works great for marine trailers with surge brakes 2 Tail light wires of wishbone-style harness make wiring your trailer more 5 wire trailer wiring harness | eBay www›Search›5 wire trailer wiring harnessFind great deals on eBay for 5 wire trailer wiring harness. Shop with confidence. Skip to main content. eBay Logo: 5-Way Trailer Wiring Connection Kit Flat Wire Extension Harness for Car Boat See more like this. SPONSORED. Trailer Wire Wiring Harness 4 Way Pin Flat 60" Inches 5 Feet. Brand New.