This is a totally non standard plug / socket. I have been unable to find any more about this than the Yaesu part number: FD10PS-6M. Any assistance would be most welcome.
Never ground pin 5 as damage to the regulator will occur.
|6 Pin undefined||Pin||Signal|
(connect to pin 5 for Up)
(connect to pin 4 for TX)
(connect to pin 5 for Down)