2018 Chevy Trax

Hey so I’m at a lost. Originally my heater went out completely. I replaced the blower motor and it worked again. Then 3 and 4 stopped working. I replaced the resistor and it worked fine then went out again. Found out the wiring harness that goes to the resistor had burned where it plugs to the resistor so I replaced the wires there. Now it only works on 1 and 2. I’m lost where to go from here.