Just My Two cents,
I think your on the right track makes sense that the 3 pin would go to the 5 pin connector. Common in aviation to have extra pin connectors that have capped and stowed wiring or dead pins. Only issue I see is there is no telling how this thing is wired internally a schematic is your best bet. There might be a simple wiring diagram inside the machine itself.
?
I know there are others on the forum with much more experience than me with this sort of thing.
Hopefully will hear from someone else with a better idea.
I think your on the right track makes sense that the 3 pin would go to the 5 pin connector. Common in aviation to have extra pin connectors that have capped and stowed wiring or dead pins. Only issue I see is there is no telling how this thing is wired internally a schematic is your best bet. There might be a simple wiring diagram inside the machine itself.
I know there are others on the forum with much more experience than me with this sort of thing.
Hopefully will hear from someone else with a better idea.