If memory serves, though it probably doesn't, that is the wrong jack for a headset mic, it is wired differently, and a headset boom mic needs to be connected to the mic jack on the jack panel, that's where you plug in your headset.
This is with the usual disclaimer that as these aircraft have 'been around the block' they can have been subjected to all sorts of modification and may well not now be as Larry Lamm describes.
