2019
If pin 1 is the GND pin for both the Molex Pico (plugging into J7) and the JST GH (plugging into a UART on the Pixracer), then pin 2 on J7 connects to pin 5 on the JST GH and pin 3 on the J7 connects to pin 4 on the JST GH.
To talk to this port from Linux, you may need to use /dev/ttyTHS1 or /dev/ttyTHS3.