[kglowacky]

on the engine side of the firewall between the dryer and the firewall there is a electric plug that has 4 or 5 wires on it, this is how the power gets to your fan motor. It is some sort of resistor as I remember. The yellow wire is the lowest motor speed . Check power to each of these. You should get power to one of these at every speed on your switch. if you don't then switch may be bad if you do then resistor is bad. Doing this from total memory as I am not home to confirm. this info based on my 78 with air. Someone jump in if my info is not correct.