Jim,
Sorry, scratch the defog relay rabbit trail off the list ... I should have read a bit more about your wiring description for the six-in connector!
Without a doubt, that connector was for a Speed Switch [aka Speed Relay, RPM Transducer] for a carbed or MFI engine from 1968 - 73.
More details in this thread, if interested:
http://forums.pelicanparts.com/showthread.php?t=216274&highlight=tach+woe