There is certainly some confusion when it comes to '65-'66 Mustang heater fans and switches. For early '65 Mustangs with center-off, two-speed fans, speed control happens at the fan motor. This means we have a three-wire motor, with two wires for speed control and one wire for ground. When Ford went to a three-speed, left-off fan switch, it went to a two-wire fan motor and a resistor pack located in the heater box. It's important to understand these differences when you are ordering a wiring system from Mustangs Plus.