The RTL brackets are mounted to the transom above the water line. This puts the Transom Lights the same height as the towing vehicle and at the back of the boat for Greater Visibility. The unique design of the T plug allows you to plug the trailer lights in also, giving you both Boat and Trailer Lights. The Transom Lights will work even if the trailer lights don't because they are never submerged in water. They are removed before launching your boat and attached before trailering your boat.