[Richard]

Johnny,

I am attaching a hand drawn sketch I made of set up similar to yours, but without a tag axle. Let's assume for a second that Newell simply duplicated the setup with the addition of the tag.
   
Then looking at my poorly drawn sketch, the regulator would limit the pressure of the supply air. The nameplate in your first photo suggests to set the pressure at 35 psi.

Have you tried backing off on the regulator and observing if the coach squats or the bulge on the tires changes indicating a weight transfer?

I don't know if  you could sweet talk someone to letting you place it on a scale, with drive tires on one section, and the tag on the other, while you tweaked the regulator?

Here is my shot at identifying the stuff in your picture. Mirror image for the left side. Always keep one thing in mind when looking at a Newell leveling system. The connection between the HCV and the air bag goes through the manifold. The HCV has it's own air supply line, but the HCV is blocked from the air bag by the manifold UNLESS the travel solenoid is opened. Otherwise, if you tried to level the coach with the air bags, the HCV would just as quickly undo the leveling.