On my headlight switch, a 1975, the only thing that does not work, is the part where you can adjust, up or down the lighting in the gauges. I'm wondering if it is fixable, or just get another one in working order?

Is that part called a rheostat?

http://www.wisegeek.com/what-is-a-rheostat.htm#didyouknowout

I don't think you can fix it but there are two pins that can be jumped to make the dash lights full bright. I have used switches if you want one.
Bruce

That's a common wear out part. See pelican. There's a tech article there on switch repair but it's easier to pick up a used one in working order.