The Longacre electric fuel pump cut off switch is designed to be plumbed into the engines oil pressure circuit (usually off the engine block or oil pressure switch, using a T-Piece connector, 1/8'' NPT thread). Once fitted to the oil pressure circuit, the switch will cut the power to the fuel pump in a crash, cutting of the fuel supply helping to prevent fires. It can also help in preventing engine damage, as it will not allow the motor to start until the oil pressure is up, and once running will shut off the fuel pump if the oil pressure drops below 12psi. The use of a momentary bypass switch enables starting or filling carburettors.