[Al Skierkiewicz]

tech,
The VBuss is measuring input voltage so that the Jag can disable output when the input power goes down to dropout on the voltage regulators. The thought being that a significant load may be causing a large voltage drop in the input wiring. By disabling the output, the voltage can climb back up to full terminal voltage. There is no feedback in the controller from the output terminals.
I changed the color on your post so people could read it.