What is a sign that air pressure is building correctly in the trailer braking system?

The sign that air pressure is building correctly in the trailer braking system is when the pressure gauge increases steadily. A steady increase in the pressure gauge indicates that air is being supplied and built up in the system, which is crucial for ensuring that the brakes function properly. In a brake system that uses air pressure, such as an air brake system, the pressure must reach a specified level for the brakes to engage and operate effectively. Monitoring the pressure gauge not only confirms that the system is charged but also gives the driver the assurance needed to proceed safely.

Other options may seem relevant to the system, but they do not specifically indicate the air pressure status. For instance, the illumination of all trailer lights indicates that the electrical system is functioning, but it does not provide information about air pressure. Similarly, observing that the air supply knob is engaged suggests that the system is set up for air supply, but does not inform on whether the air pressure is actually building up. Finally, the smooth rolling of the trailer when pulled could mean that the brakes aren’t engaged, but it does not provide clarity on the air pressure within the braking system. Thus, tracking the pressure gauge is the most direct and informative method for ensuring that air pressure is building correctly.