Hey all,

While experimenting with a rapid start ballast, when one tube was removed from the red side the blue side tube glows dimly, but when removed from the blue side the red side tube shuts off. Why is this? Anyone got an internal schematic of an advance mark 2 ballast?

The 'red side' has a small capacitor in parallel with the lamp, there as a starting aid.
That's why you get a dim glow from a lamp on the 'blue side'