In your post, you indicated that the pins 1-3 are undefined.
I managed to check the pins on my Jornada 568 sync cable & found out that the pins 1-3 correspond to the pins 1-3 on the USB port/connector of the cable.
568 connector USB connector
1 5V +
2 USB Data+
3 USB Data-
4 Ground
Information updated.
Thank you.