Get your test light and see of the fan motor is getting power and has ground. If so, and it doesn't run, it's failed. If there's no ground circuit, trace it back to the ground point, if there's ground and no power, trace power circuit back to the switch. Or test the switch first, if there's no pwer to the blower. It's most likely the switch or the motor. there's a resistor involved for the different fan speeds, it may be bad but usually it'll run only on HIGH when the resistor fails. If you can't figure it out, go to a ford specialist or an auto elelctric shop.
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