| A stupid question but what you write is you looped the db25 pin 14 but you don't tell what did you do for the db25 pin 15.
Pin 15 is the positive wire for the microphone, it also feeds DC for the pre-amp stage at the microphone. The drive voltage and the signal swing may not match your BT HF kit but it should not harm trying.
If you did loop both wires and applied the correct polarity, I guess you checked that the microphone is present (I guess you did have the full HF kit and then it of course would be present). |