[tgr131]

John -

So this may be more of a "learning exercise" or thought experiment at this point, as the junction is under the coil assemblies for the pushbuttons, and I keep looking at my friends nice work and not wanting to bungle it.   I do want to learn, and understand the process.  I may yet give it a go.

I believe I've found the junction (see attached photo). 

R39 is on the left.  C38 is on the bottom right, barely visible.  The other end connects to a different terminal lug, which connects to the wire that leads to the top of the volume pot.  (this was the wire in the previous post that I "didn't know where it went )

What confused me was R37D, but I think I understand now.  I was looking for a 47k resistor, but it appear that's inside of the 2nd IF assy, and the black wire is actually what I should be looking for.  It's connected to the Junction as well.  Do I have that right?
   

The other question I have is about "shielded wire".  I was planning to use an off the shelf aux cable, with L/R tied together through 100 ohm resistors, and possibly another 500k resistor and a .02uf cap (tied to top of pot) , and the ground wire tied to bottom.

Clipping this in with test leads, this generally works well for the aux audio, but decreases the volume for the radio stations and introduces hum if the jack is not plugged into a source.  I assume I've introduced a "ground loop" that you mentioned, but I don't quite understand the concept yet, or how to look for them and solve them.

Thanks for your patience and sharing your expertise. 

David