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Old 02-08-2013, 04:06 PM   #8
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Originally Posted by Capt. Obvious! View Post
Why would an alternator only work when the voltage regulator is unplugged

When the car is running and the voltage regulator is plugged in with the three wire connector on the back of the alternator it does not put out any voltage and the battery voltage drops to 11.92v. There is no indicator light on in the dash, but both my DVOM and a Snap-on battery/alternator tester confirmed the alternator was not working with the voltage regulator plugged in. I checked continuity from the alternator all the way back to the pcm on the gray and blue wires and they both had a good connection and the red wire had good continuity and voltage.
If I unplug the voltage regulator the Snap-on tester showed the alternator as good, but the indicator light on the dash lights up.

All I can think of is maybe the PCM needs reflashed or replaced??? It does have a custom tune by FSWerks for the supercharger. Is this a likely culprit???

I'm at a total loss, please help!!!
Could your voltage regulator need replacement, too? I've had alternators and voltage regulators go out simultaneously, and it was a "Which failed first?" type of question.

EDIT - Nevermind. Looks like it's integrated into the alternator on the Focus.
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