I've read about how the instrument dimmer on the headlight switch goes out and can't easily be repaired.
Gill Baumgartner even recommends shorting out the rheostat alltogether. That seems a little severe to me! I decided to see for myself after my dash lights flickered out, and no jiggling of the headlight knob would bring them back.
I've found that maintaining the rheostat is remarkably easy! Of course, you need to push the "secret pin" under the switch to pull the knob, and you need a tool to remove the switch. After that, it is a simple matter to remove the rheostat ceramic disc, sand the corrosion off of coils on the disc and the contacts on the switch, and put the whole thing back together. Here are some pics... first the switch removed from the dash

and the rheostat ceramic disc removed from the switch assembly

the switch without the rheostat

sanding the coils on the rheostat

and sanding the contacts on the switch. There is one contact on the side near the connectors, and two contacts on the side opposite the connectors

After reassembling the switch and reinstalling, the dash dimmer works great!
What was I so afraid of?