With the engine running at 2000 rpm and accessories on:
Set your voltmeter to 2 volts on the DC Volts scale.
Connect the voltmeter red lead to the output battery post (B+) on the back of the alternator.
Connect the voltmeter black lead to the positive (+) battery post.
Make sure your voltmeter leads are away of moving engine components.
Then check your voltmeter readout.