Headlight switch and instrument lights??

[GTXracer]

 I posted a couple months ago about my '86 Chevy Surbuban electrical woes. It seems we have finally fixed most of the problems except the headlight switch. We changed the switch several times however the dimmer still doesn't work. Turning the knob right or left should dim or brighten the instruments panel lights. The lights only brighten slightly as you get almost all the way counter clockwise. As before, I hate electrical problems. I drag race, build my own engine and do most of the mechanical work. All I know is what is supposed to happen when you pull/push a knob or flip a switch. Anyone got any ideas?  Bob

[Captkaos]

If it is orginal to the truck that part may be worn out or shorted...