If I have an external board which has 2 pins, ground and pin16 which I want to short (as would a mechanical switch) from the Pi, can I link grounds from the Pi to the external board and use the fact that pins 2 & 3 have pull up resistors on them, then send them low and that will effectively short the 2 pins on the external board?
The external board has this diagram:
COM is described Comun (-) .. Its in Spanish where Comun is Common in English.
And I would like to replace the switch show on pin 16 with a Pi:
Some other bits that I imagine are important.
Voltage on pin 16 when not connected = 12V
Current between pin 16 and Com when shorted 1mA (as well as I can measure it)