?

You also need to supply DC ground to the "GTRX" solder pad, and +5 Volts to the "5V" solder pad on the Digi board.?

This powers the output side of the ADUM4160 USB digital isolator chip (U3), for the USB CAT control interface to the Arduino.
The isolator prevents 5 Volt back-feed to the input USB connection from the PC.

?

The green wire on the dial encoder plug to the Raduino board is + 5 Volts, and the adjacent yellow wire is ground.
However, in my V6 kit, the green wire was cut off;?
so I obtained +5 Volts and ground by carefully wrapping and tack soldering wires around the pins to the 5 Volt regulator on the Raduino board.

You may find the Assembly and installation video from The Elekitsorparts Store

useful, at 26 August 2019 1:41

See the attached wiring diagram from the video:?

??