It has nothing to do with the audio panel. There is a "transmit
interconnect" wire between radios. It doesn't always get installed. I had to
have one retrofitted after completion of my Garmin 430---King KX-165A
installation.

With such an installation, wouldn't each pilot be frustrated while the
other pilot is transmitting, defeating much of the purpose of the split?

Jose
--
He who laughs, lasts.
for Email, make the obvious change in the address.