A pressure switch should always be used in conjunction with the Universal in-line Electric Fuel Pump. I.C.C. Motor Carrier Safety Regulations stipulate that fuel pump must not continue to operate after the engine stops. The Safety Interlock Circuit stops the electric fuel pump when the engine stops even though the ignition switch is not turned “OFF”. This complies with the I.C.C. Safety regulations.

The pressure switch is a single pole double throw diaphragm actuated switch. Terminals “P” (Pump) and “S” (Start) are normally closed, terminals “P” (Pump) and “I” (Ignition) are normally open. This allows the fuel pump to operate and fill the carburetor while the engine is cranking. When oil pressure exists (2 - 4 ½ P.S.I) “P” and “S” terminals are opened, and “P” and “I” are closed. The diaphragm is tested to withstand pressure up to 150 P.S.I.

If the oil pressure drops below 2 P.S.I. the connection between “P” and “I” opens and the fuel pump stops. This also protects the engine from several damage if and oil line is broken or the oil level in the crankcase becomes extremely low.

Full battery voltage must be available to the pump when the ignition switch is in the start or run position. Do not connect to the ignition coil as a ballast resistor may be built into the wire.