deuce_roadster has it, that is a generator regulator. It will almost certainly be a 6V positive ground unit since it lists Zephyr along with Ford and Mercury. The Zephyr was long gone in the USA by the time Ford went to 12V.
Sorry on the correct name on the part.
I guess its not a Ford part but one saw it here today ( rather knowledge in old hotrodding ) and he thought it was or came from Ford.