1. Yes, there is a scale light inside. You should be able to see it if you take out a couple of buttons in the middle. Not sure if you'll be able to get it out this way, though, especially if it has not been serviced in a while. Mine was stuck in the socket, and very hard to remove (it still works) when I repaired the radio.
2. Is this the C-1808 model? The speaker wire + power comes out from the top, so this little plug must be something else. Although, 3 prongs do look like the speaker plug. Maybe this is for a secondary speaker or diagnostics, or something like that?
You might want to read through the schematics: http://www.nostalgiaair.org/PagesByModel/954/M0013954.pdf
Added later: upon further inspection, this is not a speaker plug; it is a 5-prong connector, two of which are jumped. So this must be some technical switch for who knows what. I would not touch it.
Also, it looks like your button tags were re-done, at some point. This looks like the typewriter font