Re: '69 rude cut-out switch
Really not complex at all. The hose goes to a nipple on the intake manifold. During periods of abnormal high vacuum as with a run-away motor, the switch senses the high vacuum and shorts out one set of points till it slows down to a safe speed, then opens to resume normal operation.
The whole thing is mounted on a plastic plate to insulate it from the powerhead, and is grounded through the safety switch only at low throttle settings. This is to disable it at high throttle settings.
The same safety switch also keeps you from starting the motor at high throttle settings on electric starting models.