I have a 2009 e-250. I kept frying selector switches. Today I discovered why. The wiring harness that connects to the resistor that mounts on the hvac box near the blower motor behind the battery was stuck on the resistor. I had to cut the plastic off of the resistor and pry the plug off. One of the tabs broke off. I had to remove the individual connectors from the plug to remove the broken tab. They were literally rusted together. I cleaned those and replace the resistor,selector switch, and plug to the switch. I used (as one should always do) dielectric grease. I have full function and it should never be a problem again.