[Richard]

Yes, that is the correct diagram.

Of course Newell added some embellishment. One air line leaves the six pack, that tees to feed the tanks for the drive and tag. Before the tag line gets to the tag tank it has two three way electrical valves in it. One of the valves is plumbed to coach air on the third port. So that when the valve is actuated by the switch on the dash, it closes the path to the six pack and applies coach air to the tag. The second valve is plumbed so the third port is open to the atmosphere, so that when that valve is actuated, the path to the six pack is closed and the pressure is exhausted to the atmosphere.

The one thing that will throw you a loop is that you will see only ONE tag axle tank underneath the coach. That tank is bifurcated, meaning it has a plate welded in the middle. What appears to be one tag is actually two.

It took years to noodle this out, and Steve Bare @rheavn did the heavy lifting spending hours under his coach figuring it out.