Yes, the rheostat is a variable resistor. The more current that passes through it, the hotter it gets.
I have not been happy with the rheostat in my truck. (I have also found them troublesome in other older cars). To me, "rheostat" may be a curse word in some foreign language. In this truck, I thought I had it working OK, but last time we were out in the evening, I turned the lights on and there were no instrument lights. Turning the rheostat madly back and forth did not clean the contacts and bring the lights up. I couldn't find a sweet spot where the instrument lights lit up so we drove home without them. Next day, I moved the instrument light wire under the same screw as the tail lights. So now the instrument lights are not adjustable, but they work.
My solution is to simply connect the instrument light wire to the same point on the light switch as the tail lights. Who needs a rheostat!
