Fan/blower speed not working at med/high setting

[Jeff65]

Likely. Try this: remove the umbilical from the resistor so just the prongs are showing. Jumper 12 volts to each one of the prongs in turn. Fan should run at high, medium, and low speed. If this works, then switch is likely bad...problem can only be in the umbilical or switch.

Note: do not try this on other model year Mustangs. Some require power to be connected to the resistor and some require ground to be connected depending on year model. According to a schematic I have, your's requires 12 volts to be applied. Hold 12 volts on tab only long enough to hear motor speed up. If it doesn't speed up immediately, then remove jumper immediately.