Aux. Audio Input

Does anyone know what the AUX. AUDIO INPUT pin is used for on a comm. I'm
trying to chase down a problem with my two comms. I have a switch to
flip-flop between the two comms. Everything checks out good on the switch.
However, I'm receiving on both comms. I also have a toggle to turn on an
Aux speaker on and off. I think my problem is with this circuit. When I
chase the circuits on this switch, I'm getting ground shorts on other pins
that I shouldn't. I think my speaker is grounding out.

I should be able to isolate the problem, but I'm not sure what the function
of an AUX. AUDIO INPUT is used for in a comm radio.

Thanks

Eugene Wendland