What would give the driver a false indication of a Main Reservoir defect?

Turning the Tow Cock to the rescue position may lead to a false indication of a Main Reservoir defect because this action changes the typical airflow and pressure dynamics within the system. The Tow Cock, when placed in the rescue position, reroutes air flow to different components, which can affect the way pressure levels are registered on the gauges. If the gauge readings are adjusted by this modification in routing, it could mimic the symptoms of a defect in the Main Reservoir, thereby misleading the driver about the actual state of the system.

On the other hand, a clogged filter would generally lead to a noticeable decrease in air flow or pressure, rather than a false indication. Improper gauge calibration would present confusing or inaccurate readings consistently, rather than simulating a specific reservoir issue. Insufficient air pressure could lead to operational problems, but it would typically be attributed to low pressure scenarios rather than a misunderstanding of the condition of the Main Reservoir.