if the blower only works on high, that means the blower motor is good. if none of the other speeds work then the resistor is bad. 12 volts run directly from the switch to the blower motor that gives you high speed. for the lower speeds the switch sends current through a series of coils in the resistor, depending on which switch position, makes the different fan speeds. sounds like you dont have any current leaving the blower resistor. the resistor is located in the heater case on the passenger side behind the black "bubble" shaped shield. do not run the blower with the new resistor just hanging down under the dash. it will burn it out quickly. it needs the cooler air from the blower to pass over it to keep it cool.