Low air pressure switch. Normally open contacts close at 60 PSI rising. Switch contacts rated 5 Amps at 24 V DC. P/N 11669414-1, 12375453, alternate numbers SM-1A60RTP, PS4141. NSN 5930011890494.

Made in USA.

This switch directly replaces alternate style switch that has short wire leads with connectors on ends.

M939 series has two of this switch per vehicle. They are wired in series. These switches provide one of the inputs to the fail-safe warning control unit.

Switch is not for the M35, M54, or M809 series trucks.
But will work as a brake light switch on all trucks if you have 60 lbs of pressure