it's possible the tab on the rheostat 'rotor' isn't making good contact to that terminal [bent or burnt], but if the dash lights work I'd suspect other problems - assuming you've found the wires where they come out of the A pillar to the switch, take the ground wire off the switch and touch it to ground - if it works, then carry on to the switch, if the light doesn't work then one of the wires to the light is bad or you have the hot wire on the wrong terminal
Bill
