How do I properly ground my lighting system?

Make sure white ground wire on main trailer plug is making good contact to the trailer’s tongue. Also both tail lights have a white ground wire which must also make good contact to the trailer’s metal tail light bracket. Clearance lights with single wires must be anchored directly into a metal fender bracket. They cannot be anchored to a plastic fender unless a separate ground wire is ran from the stud of the light to the steel fender bracket.