2 Radios plugged into 1 Speaker?

I agree with 67Dart. Just because you can or because it might work why not just do it right. Also absolutely no to the diode thing. In it's simplest form the diode rectifies AC to DC, every look at a power suply, AC out of the transformer through the diode and you end up with DC. Audio is AC so no go there. As to the AB switch, ther are a number of different types out there and you would have to try and pin out what wires went where even then I'm unsure how many of them switch. Keep it simple and clean with either the switch or relay.

Bobby Y