There are just a few thing's that cause this, one is the voltage regulator is failing and the other is one phase of the three phase Alternator is open, u will need to have the alternator windings tested for continuity and shorts to ground, also a unregualted voltage test to determione if the voltage regulator is the problem.
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There are just a few thing's that cause this, one is the voltage regulator is failing and the other is one phase of the three phase Alternator is open, u will need to have the alternator windings tested for continuity and shorts to ground, also a unregualted voltage test to determione if the voltage regulator is the problem.
then it is not the regulaor, the alternator has a defective field winding