BMW X3 Trailer Wiring | etrailer Trailer Wiring Harness Make installing your trailer wiring harness as easy as possible with a custom fit wiring harness. Trailer wiring from Draw-Tite, Curt, Pollak, Tow Ready, Bosal, and Hopkins eliminates or reduces the need to cut and splice wires. It also helps to protect your vehicle's sensitive electronics from mis-wired trailers. trailer hitch wiring harness - Bimmerfest - BMW Forums May 13, 2014i just purchased a 2006 x3. it came with the trailer hitch, but there isnt any wiring harness. is this something i can purchase myself and install or do i need to take to bmw or some other type of shop? the local uhaul dealer said they could not do it. thanks.