Austin
FTF's #1 Knob Polisher
Looks like I'm late to the party on answering this, but I run an original radio in my truck. I love the vintage look and sound.
Agree that "A" is tone adjustment, and "B" is presets.
Mine does not have the other switch. Mine is the plain factory radio. The one you have is a factory STEREO. Since you have that switch and I don't, maybe it has something to do with the stereo?
The other switch, I have determined, is the balance left and right.
I still can't get the presets working for me, though!
