• Before cutting the headphones wire I was able to plug them in and select them as the mic source.

    However, after snipping the wire when plugged in they no longer appeared as a mic choice. The computer did acknowledge that headphones were plugged in (the output pane changed to show headphones rather than built-in speaker), but it doesn’t see it as a mic.

    I’m wondering if maybe the MacBook is expecting something that we’re not giving it? Perhaps I need to cut the cable before the Y and connect all of the grounds?

    This is maybe a little silly, but I also have a female terminal block trrs audio adapter and an actual oscilloscope. I could try reading the signal on the oscilloscope which should tell us if the wiring / circuit is ok.

    If it is, then I would assume that there is something magical that the MacBook is looking for to recognize the line in. It’s clearly looking for more than just a trrs cable plugged in.