I just did the G and IN bridging test and so effectively the laser does not activate when I press the test button.
What I don’t understand is that if I leave IN without connecting anything, the laser is activated with the test button.
I don’t recall if there is a pull down resistor on that control line but if you are skilled in reading schematics and understand electronic control logic the schematic of that area is posted on the forum somewhere and probably on Don’s blog too. Think of it this way, it is one of two laser control signals so you need to purposefully control each pin. A POT connected as in the drawing you posted should provide that level of control. ie when it reads 0V it also means the IN pin is connected to the Ground pin by the POT.