[GreenKeys] Four-prong wiring question on M19s...

[E.]

Question…

I’m trying to figure out the wring on a certain 19 table.  The 19 that came with it (thanks Paul ^^ !!!) has the rare four-prong plug, along with a even rarer, loose four-prong female socket (that connects directly into the power mains junction box on the table... I have seen wire clamps on these table boxes before without this attachment, so this is new to me), in addition to the four-prong female socket belt into the table.  I know there are wiring diagrams - I have looked at them.  Both four-prong sockets seems to be wired slightly different on the ohm meter (the wiring diagrams do not include this loose socket - they might have been added later)… so I guess my question is and so that I can further figure this out (the 19 has an alternative wiring scheme which is not diagrammed either) - what was the purpose of the four-prong male plug in the first place ;o ???

Thanks much as always in advance ^^ !!!