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...
Do you mean this? (My attempt to understand your diagram)

1
2 3
4
5 6

1 = Down button (12V to activate)
2 = PTT line (ground to transmit)
3 = Up button (12V to activate)
4 = GND
5 = Mic-level audio
6 = 12V power (regulated to 5V inside handset)

Yes, that's correct. Thanks for clearing it up a bit. Your diagram is
definitely easier to understand than what I did.

-Greg