the little light under your fuel gauge (green) is a turn signal indicator. It blinks to show that the signals are on either left or right. You are correct about the instrument panel lights. They are the grey wires that are single. If the park lights or headlights are on the will come on. you can adjust strength of the lights by turning the dimmer switch (headlight switch) to the left or right. All the way to the left will turn the dome light on. I have a nice unit that came out of my 63, which is the same if you need a better cluster, minus the fuel guage. Just let me know. I can send pics if you need. Or you can do a wire conversion and swap in a set of the factory guages, which will give you a more accurate reading of the engine.

http://s971.photobucket.com/albums/ae197/jon63c10
1963 c-10 shortbed stepside 427 BBC T16 HD 3 speed
1963 c-10 shortbed fleetside 348 "w" 1st gen big block & powerglide