now this sounds dumb, but make sure knob is not all the way dimmed... OK, But I had to ask.
Look with test light on both sides of fuse you changed. Is it hot on one or both sides????
If hot on one side , fuse in no good, if hot on both sides , go to new switch and see if hot there.
If fuse is not hot on any side, you have blown a inline fuse under hood or in another fuse box.
Did this just happen all at once, or I bet someone put in a new radio or did some work on ash tray or c.b. radio.
Has anything been fixed or done anything to at all on truck in last month.. new radio for Christmas???????