U-Haul: Moving supplies: Wiring & Lights U-Haul 4-Way Flat $16 FREE In Store Pick Up . U-Haul 4-Flat 4 Way Flat Wiring CQT118300 4-Flat with Factory Style Tailight Harness $22 FREE In Store Pick Up . View all Quick Connects. Have questions or need help? Chat with a moving expertU-Haul 4-Way Flat · TrailerWiring Adapters · 60” Lead · Universal Trailer-Wiring Harness U-Haul: About: How To Install The Quick Connect Trailer Make sure that the trailer’s wire harness has adequate length to reach this point and mount the adapter. 2. Plug the 4-flat plug of the adapter onto a 4-flat plug extending from the vehicle. This will provide tail light, left and right turn functions.