The microphone audio and PTT is done in hardware, i.e. the red straps inside of each RRC.
It appears that somewhere there was a mistake in the wiring. It must match that provided on
page 115 of the manual. The Icom is however the easiest one with the wires just going straight
across, so perhaps one or more of them are not installed correctly. Use an ohmmeter to see if all
are connected properly. When installing, never use your fingers, instead hold the strap with
needle-nose pliers just above the start of the insulation and gently push into the hole. If the wire
gets bent, throw it away and set a new one.
I hope that this helps.
73,
Mitch DJ0QN / K7DX