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Under normal conditions alternator seems to work fine charges between 13.2 and 14.1 volts. As soon as I turn on the blower motor (as in using heat or defrost) charging drops as low as 9.5 volts even at highway speeds. I have replaced the alt. 3 times but still the same problem.
Any ideas, I was thinking faulty blower or maybe the speed control under hood.
Vehicle is 1990 Bronco, 351,E4OD,full power.
Last edited by Gooch; Sep 29, 2004 at 07:57 PM.
Reason: forgot to add vehicle info
So if you turn your lights, wipers and other loads on, the voltage stays up? If so, then I agree you might have a problem with the blower motor, though you would think if it was a real problem it would blow a fuse.
If the voltage drops no matter what load you have, I would un-wrap the wiring going from the alternator to the wiring that goes to the starter relay. Look for a corroded connection. There is a factory splice in there somewhere.
Thanks for your responses. Took the blower moter out this past weekend, and found a mouse had some how got in to the fan and got caught between the fan and the plenum causing a drag on the motor.
Must have been the problem, after removing the mouse,cleaning 14 yrs. of crud off the fan blades, I reinstalled and voltage doesn't go below 13vdc.