Review on DOT Certified 4-inch Round LED Trailer Tail Light Kit with Red, Amber, and White Lights - Includes Grommets, Plugs, and IP67 Waterproof Design for RV Truck by Jorge Kumar

Whatever other reviewers say, don't oversize those headlight holes! The socket is sized to fit a 4 and 1/2 inch bore. After cutting the hole, insert ONLY the rubber grommet (big black ring around the light) into the hole, making sure the grommet "fits" properly and the small flexible flange on the grommet extends beyond the hole. This flange slides through the hole, but it has to wiggle and pull a bit to get it all the way through and into place properly. Once the socket is installed in the hole, insert the light assembly into the socket. Some force is required to ensure the light is fully inserted into the sleeve. To remove the lamp, push from the rear (if you have access) or gently pry the lamp away from the socket with a plastic front trim tool.