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If the answer below doesn't solve the problem, have the alternator checked, as the regulator may not be working properly. Have it checked fairly soon, as fluctuations like those you describe can harm the car's computer and electronics. Clean both battery cables good and make sure there is a good ground between the engine and body. This ground is important so make sure it is tight and clean {no paint or grease}

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2006-12-18 03:00:22
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Q: Why would the voltage indicator fluctuate between 15 and 18 at all times and all lights go bright then dim and the battery light flash?
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