Tips for Installing 4-Pin Trailer Wiring | AxleAddict Jan 18, 2019Buy a 4-pin wiring kit with wires at least twenty feet in length, so it's long enough for your trailer. The most common wire thickness for a trailer is 16 gauge, but I bought thicker wiring for added durability. Depending on the size of your trailer and the number of lights, you might want to check on the Internet for the recommended gauge for your specific trailer.Author: Matt G. 4 Prong Trailer Wiring Harness | etrailer 4-1/2" x 5-3/8" Square trailer tail light is submersible. Integrated LEDs indicate if there's a fault in your trailer wiring trailers more than 80" wide. Includes replaceable Light accepts industry-standard 3-prong plug PL-3 pigtail harness included for trailers that don't have existing plug Surface mount with included studs Designed for trailers more than 80"