Low Pressure Switch, Normally Closed Low Pressure Switch, Normally Closed Low Pressure Switch Normally Closed, Closes 8 psi. Opens 20 psi., 7/16" x 20 Thread 18-03599 - Low Pressure Switch, Peterbilt Low Pressure Switch Normally Closed, Opens 25 psi. Closes 38 psi., 7/16" x 20 Thread