73 challenger hvac blower inop

Got a little confusion my blower for the hvac wouldn’t work so I confirmed the motor was good and went to the switch where I found the three female electrical connector melting and one of the male connections on the switch melting and there were no blown fuses so I removed the 5button switch and trying to find the correct switch at the best price so my question is what caused the short with so many different part numbers the correct switch to get thanks for any imput
Author: HYDRO