howard winwood G4GPF
I can answer you, the mike has 2 connections, the ptt switch has 2 connections, for the mic one of the connections on the base goes to the metal body of the mic and should be connected to ground/earth/0 volts.
one side of the ptt switch goes to the ptt pin the other side goes to earth/ground etc so two wires go to one connection the earth/ground connection.
that’s why you only need 3 wires total for mic and ptt.
I don’t think I can add any more to that, that would explain it any better.
I think you are trying to overthink the problem, the wiring diagram shows only 3 wires from the main board, one of them earth/ground, that one MUST be the common element .