Low air pressure switch. Normally closed contacts open at 60 PSI rising. Switch contacts rated 5 Amps at 24 V DC. P/N 11621847, alternate numbers PS2061, SP-1B-60RPP. NSN 5930004345441.
Switch controls the low air buzzer (and low air light if equipped).
Not for M939 series.
Can also be used to sense fuel or oil pressure in alternate applications. Mating electrical connector is MS27144-1.