This accessory socket is a convenient addition for running all of your 12 volt accessories like your cell phone or MP3 charger To install it, put the barrel in from the front side of the hole. The collar threads on from the rear and holds the socket in place. There are two 1/4 inch quick connect tabs for connecting power and ground. This is what's called a safety socket meaning it won't work with a cigarette lighter element. I guess it's a way to keep the kids from burning their hands or starting the car or truck on fire. The weatherproof rubber cap keeps out water and debris.