[justinn]

If you have an issue with the dash A/C fan only working on High, I found a cross reference for the resistor(there are two if you have passenger controls also).

Motorcraft D8BH19A706AB    or D8BZ19A706A  for a 1979 to 1981 Ford Mustang

I have attached a picture of the back side which shows the plug configuration. I am sure there are more cross-references out there, but I have verified this works. Setting 1 and 2 may be the same speed(hard to tell), but 2-4 definitely increase blower speed. I have tested this for a couple of trips and everything is working great.

   

[justinn]

I forgot to put the location in which to find the resistors. They are attached on to the blower assembly behind the radio(center console), at the very back at floor level. You will see some relays on a panel, these are in the center of that panel. Access is a PITA if you try to access through the radio hole or the teardrop access under the switches on the center console.