[Richard]

Ok.

Let's start by ensuring the tag axle switch on the dash is in the center position. If it is not then place it in the center position.

That switch is used to let air into or out of the tag air bag independently of the drive bags. By placing air into the bag you can remove weight from the drive axle. Handy if crosssing Ohio turnpike scales which might flag you as slightly overweight on the drive axle. Or if stuck you can remove weight from the tag, putting more weight on the drive axle. Useful for snowy or icy, but careful if using that in mud or sand. You only dig deeper.

The way it works is that two solenoids are placed in line between the supply tank for the drive air bag and the supply tank for the tag air bank. The solenoids are THREE WAY. Important to keep that in mind. One solenoid valve is normally open to the drive tank and tag tank, when activated the port to the drive tank closes, and the third port is normal supply air. When that solenoid is activated, the path to the drive tank is closed and now the tag tank is getting 120 psi supply air.

The other three way solenoid normally connects the drive tank to the tag tank. However when it is activated the other port is exhaust. So when activated, it closes the tag tank from the drive tank, and connects the tag tank to exhaust the air.

If the tag switch is in the middle position, and the coach is in travel mode, does the tag bag inflate? Very important to answer that question before proceeding.