Wishbone Wiring Harness | etrailer 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 Amazon: wishbone trailer harness Socket Adapter 4 Pin Exterior Flat Wishbone Style Trailer Connector Wire Harness(96×3cm) by EDIONS. More Buying Choices $4 (1 new offer) Wesbar 4-Way Flat 25 FT. Trailer End - Wishbone Harness - 3 FT. Ground consumer electronics Electronics. by Brnadzs. $25 $ 25. 80.