Ok, then it really looks like the vacuum circuit for the cutoff is in place correctly. If the other vacuum powered accessories work (climate control, door locks, transmission shifts well) where should I look for the problem?

Could the cutoff actuator die so suddenly and without warning? Any way to test the ignition switch to be sure it's doing its job? I am having some trouble with the switch - it's really finicky on turning all the way to START at times.