[dmjlambert]

The 12V+ comes in on terminal 1, then goes over to this thin rectangular device attached to the case on point 2. I think that is some sort of filter. It does not ground the wire, but it is close to ground. Perhaps some sort of spike protector. The other side of it is a blob of solder on the case outside under the label. From there it goes to the switch that is on the end of the 2 gang potentiometer, point 3. When the volume knob is turned up to click the radio on, I should get 12V on point 4, but I do not.

If I connect 12V+ directly to point 4, the radio tests OK, it just won't turn off without me disconnecting the battery.

There are 2 wires connected to point 4, to go to the radio light bulb which goes outside of the case and around back of the radio on the brown wire (5B) and to go to the choke (5A). Coming out of the choke the red wire 6 goes to one of the terminals on capacitor 7, visible from the top side.

So that rectangular plate, choke, and capacitor appears to be noise suppression and filtering at the input power supply.

It looks like I would have to unsolder about 5 or 6 connections on this gang potentiometer and switch before I could remove it to get to work on it. There may be some tabs I can bend to take it apart and examine the inside of the switch. Maybe I can remove 50 years of tarnish and varnish and make the contacts work.