Vehicles with air brakes are equipped with a low air pressure warning device. It will activate a red warning light on the dashboard if air pressure in the primary or secondary air tank has fallen to 414 kPa (60 psi) (although some manufacturers’ systems activate at higher pressures). If this happens, you should brake safely to a stop and repair the problem before the air pressure drops to the point that the service brakes won’t work properly. Note: On older vehicles, a “wig wag” (mechanical arm) may activate instead of a warning light.