A low warning switch is installed after the supply reservoir to alert you when air pressure drops below a safe level 60 psi (414 kPa). The switch activates either (or a combination of) a buzzer, warning light or a wig-wag (a “flag” that drops into the driver’s view). If the low warning system activates, you must stop and determine the cause. The warning light must be operational. The buzzer/wig-wag are optional.