If it's actually putting out 16 volts - beware! If this is a permanent Volt Meter such as a fairing mounted gauge, make sure it's reading correctly. Double check with a Volt Meter at the battery when that's happening.
If it is actually putting out that much voltage, the regulator would be the first and primary suspect!
Wanted: Dead, smashed, crashed or trashed gauges
BMW GAUGE REPAIRS - TACH*SPEEDO*CLOCK*VOLT METER *PODs & LIGHT BOARD*