2002 Dodge Stratus something wrong with my car heater

I have a 2002 Dodge Stratus. The heater only works on #4 not on 1, 2, or 3, if I cross the terminals on the back of the switch they all work, by doing that it burns the switch out. I bought a new switch but still the same problem. It worked fine till last yr. The blower motor works fine, I tested it. What else could it be. All the wiring is good also.