Hi @CA_BlueBoat -
No, the GPIO 16 has no correlation with the Raspberry PI GPIO pins. You’ll get your output from the pin to the right of your arrow, (signal = s.)
Note that you can only draw 15mA! You’ll also need to be using the latest ArduSub (4.1.2)
To control the pin from lua, you would do something like this. Something similar should be possible to do with pymavlink and mavlink.MAV_CMD_DO_SET_RELAY