Trailer wiring and harness plugs are available in a variety of sizes and configurations. The most basic of designs is the color coded 4-wire system which uses a brown wire for tail, license, and side marker lights, yellow wire for left hand stop and turn, green wire for right hand stop and turn, and white wire for system ground. The "Flat-4" harness plug is found on almost all boat trailers and many smaller utility trailers that do not have brakes.
I think myy Nitro trailer has a 5 wire set up, it works with 4 hooked up as the last one os for disengaging the trailer brakes when backing up hill. Or at least that is what I ws told at the stealers.