A4 1.8t 96, voltage indicator problem

A friend of mine got a a4 and the voltage seems to be going a bit up'n'down. Usualy it is between 12-14v. but sometimes it slowy goes down to 8,2 (on the indicator that is).
And one time it just dropped all the way down real fast, and climbed up again. Have been trying to turn AC on/off, and the hi-fi on/off and other switches. But can't find a connection between any electric unit and the jumping voltage. Anyone who have had this problem and maybe could help me out a bit. Will get a hold of a multimeter and messure that voltage on the battery when it's going up'n'down. It happens in motion as well as still.
thank u very much!
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Mikael,
It sounds like your voltage regulator, alternator, and/or battery are on the way to the great autobahn in the sky. Many auto battery dealers such as AutoZone in the US will perform a series of tests on the electrical system at no charge. It is also possible that the gauge is faulty.
Jon jpb357atjunodotcomofcourse

up'n'down.
is).
switches.
when
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wrote:

When the voltmeter reads low do the headlights/interior lights dim in turn? Does it only happen when the engine is running?
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