dlotz -- I know there's a thread on the ERA forum here discussing the circuit, how the small charge through the filament excites the VR, etc. as I specifically remember photocopying the diagrams from my automotive textbooks that were used in the classes I took on the stuff way back in the 1970's and quipped that I must have been asleep when we went over it.
I'm sure I posted them here along with the explanatory text from the manuals. It's really a very simple, basic circuit but if the dang filament in the bulb is broken, and you don't have a shunt, you'll never get your charging system up and running.