Boat Trailer Wiring Harnesses | iBoats Boat Trailer Wiring Harnesses - Since 1998, iboats is the most trusted water lifestyle online store for boat parts and accessories, boats for sale, and forums. Enjoy great priced products with fast shipping.Price Range: $1 - $10,000 Amazon: Boat Trailer Wiring Harness Amazon: Boat Trailer Wiring Harness. Skip to main content. SUZCO 25 Foot 4 Wire 4-Flat Trailer Light Wiring Harness Extension Kit, 4-Way Plug 4 Pin Male & Female Extension Connector & Wishbone-Style with 18 Gauge White Ground Wire with SAE J1128. 4.1 out of 5 stars 68.