Volt meter down to 8V

[Denis]

The Voltmeter on the instrument cluster gone to 8 volts.

The battery voltage  is 13.4 volts went the engine is running.

It seems the voltmeter does not indicate the right thing .

Where should i began to look at.

Everything in the instrument cluster is normal, only the voltmeter gone bizzard.
I stop the car friday night and saturday it indicated 8 volt, battery at 13.4 V

tnaks

Denis