I have also seen corroded wires cause this. The wires at the alternator will corrode or break. It is not easy to see though. Your alternator is not charging at all at idle. I have done the mod mentioned by Steve, but most of the time it will be negative 2 amps, not negative 25. Check the blue wire at the alternator.

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Donnie Drummonds
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ASE CERTIFIED MASTER AUTO TECHNICIAN
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