Data Cable Pinout for Garmin Round Jacks

If you look at the jack on the G-III+, you'll see the pinout labels.  This is how the data cable is wired:
    GPS Jack CCW from key    GPS cable CW from key....Serial plug
1            Power                 Power                 None
2           Data out              Data out                 2
3            Ground                Ground                  5
4           Data in               Data in                  3