69 C-10 Knob Question

I'm new to classic trucks so forgive my ignorance. I posted this to alt.trucks.chevy and got no response so I thought I might try here.
To the right of my climate control levers in my 1969 C10 is a little nub.
After looking at pictures online it appears some sort of knob or dial belongs there. Anyone know what this knob or dial was for?
More info: This twist knob (or where one should be) sits opposite of the keyed start, seated in the truck the key hole is left of the climate controlls and this thing is to the right. When I look under the dash I see (I think just took a quick look) two wires terminating there? Is this an A/C knob? My truck did not come with factory A/C fwiw.
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I wish it were so simple :) If this was the original location for the lighter on on a '69 someone started a stock looking mod with some sort plug/switch there. Is it possible that having a lighter was an option and if not equipped they just ran the wires to a dummy plug?
.....

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