85/105 PSI Pressure Switch. Heavy duty tank-mount pressure switch 2 Male spade style terminal for wire connections. The pressure switch receives 12 volt ignition power and sends signal to a SPDT 30/40 amp Model 340 relay that turns the compressor on and off automatically. The safety relief valve on the tank will blast off when the pressure switch fails, when you hear that, kill power to the compressor so that it doesn't burn itself out, then replace the pressure switch.