Bill KO4NR reports a successful homebrew build of MiniDin8 Y-splitter. This should work for CAT control of Yaesu FT-8xx radios and accessory port of Xiegu G90
With the exception of a small metal project box three of these connectors is all that you need.
The color code pin wiring is shown on the bottom of the connector’s data sheet. To ensure the needed connector’s pins are connected solder all the wires together using their color coded wires.
Follow up from Bill:
This shows what pins are needed for the Yaesu FT-857D to work FT-8 and keying an amp or antenna switch relay simultaneously. However I still recommend connecting all the wires on the pigtailed 8 pin Mini Din connectors. That will make the splitter box useful for other applications.
This is from the FT-857D manual.
It is important to know that pins TX GND and GND are active whether the radio’s settings are set for CAT Control or Linear.
Now there’s this cable available: