Yesterday the meter was even going to 18V and engine warning light went on with this high load.
Went today for a new HD unit and found out that the one which was giving to much voltage was not original HD but from Drag Specialties.
Now with HD unit (which was 4 times the price of the DS rectifier) gives good reading.
Wife now very happy, because she was afraid she couldn't drive the M3W Treffen next week.