Garmin Audio Panel Failsafe

I have installed a GTN650 (COM1), GTR20 (COM2), and GMA 245 (Audio Panel)...the audio panel manual says failsafe mode connects pilot headphone/mic to COM1...it also says there is a separate failsafe audio input that will also be shorted to the pilot headphone if wired. It mentions possible use of series resistors for some combinations of external radios.

Questions: If I want COM2 (GTR20) to also be heard during failsafe mode, can I wire COM2 headphone to the failsafe input without resistors? G3X, GTR20, and GMA245 manuals say nothing additional that I can find. If I need to use resistors, what values to use, anywhere to find the circuit diagrams?

Walt,
You're up.

It’s generally a bad idea to directly connect two audio outputs directly together, as output #1 will ‘see’ output #2 as nearly a short circuit to ground. And vice versa. This depends on the actual design, of course, but is a general rule. So, for your case, install a 220 ohm resistor (exact value not critical - but make them all the same) in series with each audio panel input (between the radios and the audio panel) that you intend to be connected together in emergency mode. In your case, the two audio out lines, one from each radio, each get a series resistor somewhere before they are connected to the audio panel.
1/8 watt or higher power rating.

You 'al know what I'm gonna say: Doesn't sound like a good idea to me... KISS is your friend.

+1. While I tried to answer the OP’s question, I agree 100% with Walt. Unless you are very careful to mechanically support these resistors, and protect them from vibration, the odds are they will fail (and take away that com) more often than both the audio panel and com 1 will both die.

Thanks for the feedback

Appreciate the need to protect the diode lead.