Insufficient Charging OutputIf one of the three stator windings failed, the alternator would still charge, but only at two thirds of its normal output. Since an alternator is designed to handle all the power that is needed under heavy load conditions, you may never know that there is a problem with the unit. It might only become apparent on a dark, cold rainy night when the lights, heater, windshield wipers and possible the seat heaters and rear defroster are all on at once that you may notice the lights start to dim as you slow down. If two sets of windings failed, you will probably notice it a lot sooner
It is more common for one or more of the six diodes in the rectifier to fail. If a diode burns out and opens one of the circuits, you would see the same problem as if one of the windings had failed. The alternator will run at a reduced output. However, if one of the diodes were to short out and allow current to pass in either direction, other problems will occur. A shorted diode will allow AC current to pass through to the automobile's electrical system which can cause problems with the computerized sensors and processors. This condition can cause the car to act unpredictably and cause all kinds of problems