[Fulltiming]

The red needle should be the 'primary' brakes or the rear brakes, the white needle should be the 'secondary' or front brakes. The red needle dropping out prior to the white needle would indicate a leak in the rear brake air tank (2 tanks are located aft of the generator on my coach, the one on top and to the rear is the rear brake air tank, the one lower and toward the front is the front brake air tank) or in the air lines connecting the the rear brakes, OR if the AUX tank is dropping out faster or at the same rate as the red needle on the brake air pressure gauge, the check valve located at the air inlet to the primary brake tank may be defective allowing air to flow out of the brake tank as it leaks out of the AUX air system.