Ok this one has got me baffled. I rarely replace my starter or alternator as I always just rebuild it, 20$ kit and in most cases it is good as new. This time it seemed like a simple voltage reg that went bad, I took it apart installed a new 5$ regulator and the same problem still exists. As the rpms increase voltage spikes up to 15-16v. I know the plug on the side of the alternator just goes to ground and the red wire is simply connected to the big red wire that is bolted onto the alternater so I dont see the problem. Can anyone else sugest what to try next.

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David hotrodfiero@shaw.ca
85GT 2.9 4spd

actually you have a misconception about the wiring of the alternator.

The red wire is hot all the time and does loop back to the big hot wire on the back.

Whenever the engine is running you should have 12v on the brown wire.

If you have voltage on these wires with the engine running, either your regulator is bad or something inside is grounding it out and making it go full charge and you will need to replace the alternator.

Phil

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GTDude
OVER 25 years GM experience