Jim....Yes, After the fan drops speed it doesn't matter what you do to the control. It does it on auto, with auto off, heat and cold. It will also do it when just checking the codes and running the fan speed code on #10. You can place the speed on high, the control reads 8V. The wire at the regulator reads 5.7V while running on high and then it drops down in speed while the control still says 8V and the wire reads only a tenth less, about 5.6. I have another question..When the unit is not on auto does it still work like it is on automatic varying the fan speed when the car reaches a certain temperature?

Fred...My only question is that if it was a temperature sensor would the control unit still not be giving a false reading. It would seem to me that the sensor would be sending a bad signal to the control and then it would cut the switching voltage to the regulator. From what I have seen of the circuit the yellow wire, which should be the one to control the switching of the regulator, always works as it should. If it was something telling the control to turn the fan off the switch voltage would change wouldn't it???