I have had the same problem. At first, I just replaced the switch, and in a short time, it burned up, too. While looking at it the second time, I noticed that a wire in the wiring harness inside the dash was also burned. I did not get far enough into it before I replaced the truck, so, I do not know if the burned wire was the cause, or if it was a result. I would have a look, though, because if the wiring is shorting, it could cause more vital functions to go haywire at the wrong time. You would really have to do a continuity check and short test with all of the wires in that plug. Also, check the resistor for the fan.
