1990 buick riviera 3.8l. no power to alternator switch The alternator doesnt put out any juice and the car just runs off the battery. theres a little two wire plug going into the alternator with a grey and a brown wire..As i understand it those two wires send voltage to the alternator depending on the load its bein put under. But when i run the buick and check those two wires they both read less than 1 Volt no matter what i turn on. (Radio, ac, heater) What controls that little plug? The vehicle has been parked for 8 years but still runs fine for bout 20 minutes then the batterys dead.I would really like to use this car as it only has 70,158 original miles. thanks for any assistance.

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09 Apr, 2017

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The charging system (alternator) is controlled by the body control computer .
The brown wire is the turn on signal . The gray wire is voltage sensing .input bat. Disconnect the two wire connector an use a test light connected to battery positive , touch the point end to the terminal where the brown wire would go . IF the alternator is good this will full field it an it will charge like crazy . Don't do it very long , this is just a check to see if alternator is or is not the problem . If the alternator works like that you have a BCM problem an it would be in your best intrest to take to a qualified repair shop .
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