There were two different Heater Blower Switches used for 65-66 Mustangs. The 64 1/2 and early 65 Mustangs that were built before 4/1/65 had two speed blower motors that used a different switch. This particular switch has the "off" position in the center. Up until now, these switches were difficult to find. We now have them available. Order part number IN5601.
Of course, we still have the later style 3 speed switches for your Mustangs if it was produced after 4/1/65 also. This switch has always been a very popular part. Order part number IN561.