OWNER WAS DRIVING, ATTEMPTED TO TURN UP HVAC FAN TO HIGHER SPEED BUT NOTICED THAT FAN WOULD NOT INCREASE SPEED AND STAYED ON THE LOW SPEED. THEN STARTED TO SMELL SMOKE. PULLED OVER, SHUT TRUCK OFF BUT NOTICED HVAC BLOWER FAN WAS STILL RUNNING ON LOW SPEED. SAW FIRE INSIDE RIGHT SIDE OF DASH. FIRE ORIGINATED INSIDE RIGHT SIDE OF DASH AT LOCATION OF BLOWER MOTOR AND RESISTOR COMPONENTS. *TR