What are the pressure gauges connected to in vehicles equipped with air brakes?

In vehicles equipped with air brakes, the pressure gauges are connected to the air tank. The air tank stores compressed air that is used to power the braking system. The pressure gauges provide a visual indication of the air pressure level in the tank.

The alcohol evaporator is not typically connected to the pressure gauges in vehicles equipped with air brakes. It is a separate component used in certain air brake systems to prevent the freezing of moisture in the air brake lines during cold weather conditions.

The engine is also not directly connected to the pressure gauges. However, the engine's air compressor is responsible for supplying compressed air to the air tank, which is then measured by the pressure gauges.