Why is it that automotive instrument cluster, knobs, levers, cranks, dials, etc are so weird and strange? It's unbelievably difficult to figure out how to get control knobs (headlight, wipers, that sort of thing) off when they're on the car!
Here's why. It's simple, but not obvious and impossible to see on the car. I can never remember how it works, and have to puzzle it out every time! So after 20 years, I realized I could WRITE IT DOWN. Here it is. You no longer have to resort to Vise Grips and swearing.
(Click on the photos for a very high resolution image; you'll need it.)
Left photo: There's a spring steel insert inside the back of the knob that grips the flatted shaft of the control itself. The insert is intended to stay in the knob. See the "D"-shaped hole? The flat on the "D" grips the flat of the shaft; the shaft often has notches to add more grip. It's not fully obvious, even with a close-up photo, that that part of the clip moves. See the notch molded into the plastic, pointed to be the allen wrench held in a dirty finger? That notch tells you where to put the Tool. (The notch is generally pointing toward the floor mats.)
Right photo: Place the Tool in the notch, and press it inward against the clip, HARD. This pushes the "D"-hole upward, the flat of the "D" then lifts slightly off the shaft, at which point you can remove the knob from the shaft.
The Tool is a 1/8" allen wrench. Vise Grips no more! You will still need swearing though.