What truck is this on? If it has cab air suspension it should have 4 air lines to the hydraulic valve, 2 for AOP hydraulic control and 2 for cab suspension.
if it does not have cab suspension, the line that runs toward the rear is connected to a remote control supply valve. That valve samples primary and secondary tank air, and has a control line that looks at park air. When you release the park brakes it disables the air supply to the Air op hydraulic control valve. Keeps from tilting the cab when driving…
you will need to cap that line of remove the valve it attaches to back over the rear axle and cap its 3 connections…
