Thanks all for a great start with various schemes. Using the judge version, could I use the DPDT as an audio only center point for the mods? I would lift the volume ends and take them to one side of the DPDT and back on the center of the switch. Radio remains normal at this mod.
On the other side of the switch would be the Bluetooth assembly. Hopefully it becomes an input switch with the original volume control and radio amp.
I found a $11 Bluetooth board that is USB powered and not amped.
https://www.amazon.com/Niubow-Blueto...499136&sr=8-37
Then the Bluetooth side via a $1 isolation xfmr to the second side of the switch and to the volume control. 2K resistors as needed for mono and for adjusting to any given radio as the board does not seem to have volume control. The module can also take +5-35vdc from any source. Maybe even a point on the chassis? Otherwise I would glue/wire the USB adapter to the power line for simplicity.
I'm looking at building the Bluetooth side on a small board that can velcro or glue in most any open space with wires long enough to go to a rear drilled switch. I think this clears me of any hot AC floating around that cannot get back through the transformer. If it is not dangerous I will try with a spare clock radio to proof.
Or should I buy more fire insurance?