Gene
The Air force one by demco has a couple of lines connected into the coach
1) there is an air supply line which is connected to the air supply to the air relay valve for the rear brakes on the coach this fills a small reservoir tank through a flow restriction which activates in case of large flow .
2) a smaller air line which connects to the signal line at the rear relay valve this line comes from the treadle / foot pedal ovalve at the drivers station and provides the control to both the coach rear brake relay valve and another small relate valve on the demco resovoir .
3) the final air line comes from the demco resovoir tank relay valve and goes to the rear of the coach to an air coupler for the toad to connect to.
The system is set up this way to separate the toad braking system from the coach system in case of a lose of air line between the coach and toad there would not be an adverse effect to the coach brake system according to demco this is the only DOT legal way to connect to the coaches brake system.
It is also what I installed on my coach and works very well.
Here is a video which might help
https://youtu.be/BGZQ-4pKSVIHope this helps
Eric