What does the first dial next to the headlight switch do?

[MichaelAnthony]

I like that switch very much.... I have added mood lighting and that is the switch that controls it..... snice.....

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[Joe98]

I have a Sport S. , so it doesnt do much of anything, even with lights on. I've known this, for almost 2 years.

So, which switch do you use to dim your instrument panel?