Tekonsha 12 Volt 3 Terminal Battery Switch fits all your needs. 3 terminal is for metal frame ground systems, 4 terminal has insulated ground terminal for use with fiberglass or other non-conductive materials, Includes terminal nuts and lock-washers. Nothing else to look for or buy, saves time and money. Isolates starting batter. Assures primary battery power for starting engine and provides secondary battery current for auxiliary power. Cadmium plated, non-breakable heavy duty housing. Resists rust, gives long life in most any environment. Full time charging of both batteries. Gives you early re-use of secondary battery. 12 volt DC continuous duty.