The rheostat is very sensitive, before I replaced mine there was one VERY small portion that would work near the brightest setting. A switch from Rock Auto was pretty cheap, less than 20 bucks as I recall.

If you pull the cluster its pretty easy to look at the PCB, and where power is feeding from, and then just test with a voltmeter.

Do your oil pressure light, fuel, and temp gauges work? What about the turn signal indicators? Radio?

It could be;

1) The Light Bulbs are All Bad
2) Power from the PCB to the lights bulbs is missing, either an open circuit between all of the bulb fixtures or no power to the PCB for those fixtures. I assume that power will be coming from the light switch/rheostat, I have a spare cluster I can check when I get home.

I would suspect the rheostat on the headlight switch, especially if the radio doesn't illuminate either.