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I have a 1990 Cummins cannot keep a voltage regulator in it they will last for a couple of months, then will either short to ground or open up. It will either overcharge or not charge at all.  I have been getting them from Napa,. Anyone with any ideas,  help would be greatly appreciated.

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I would have the alternator checked it might have a bad armature winding that is killing the voltage regulators. Basically, in a nutshell, the charging system has been the same for years. Blue wire is +12V key hot then the green wire is variable ground from the voltage regulator. So the blue wire supplied the sense voltage to the regulator and then the case would supply the ground for alternator as well as the alternator. So verify the green wire is not shorting to ground or opening up. Then verify the regulator case has a good clean ground contact. 

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I have checked all cables, and ran aground from the battery to the case, I will have the alternator checked. Its simple the way it works but a regulator ever couple months is getting old.


Thanks for the reply I will have the alternator checked.

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