Please help GMC Safari 99 alternator

The voltage gauge on my 1999 GMC Safari reads 9 volts; it should be above 14. I took the alternator to an electrician to have it checked, and he said it's good and charging. When I turn the key, the battery light comes on, and it goes off when I start the engine, but the voltage gauge on the dashboard isn't reading correctly. Thanks!

It is easy, check with a multimeter if you are really loading, if it is above 13.2v then it is loading, and what does not work is the engine of the board