Bought a replacement alternator but I am sending it back as I measured and have seen it running over 16.5V. The manual says the regulator should keep it to a max of about 14.5V.
I put a brand new and fully charged battery in at the same time the alternator was changed, so I don't think the battery can be blamed. Also at the time I tested it, was running as little electrical load as possible, no lights, fan off, radio off, etc.
The seller has accepted a return on the alternator, but also sent me this advice:
"if you fitted this alternator to a vehicle with a flat or faulty battery it will perform eratically . most alternators are engineered to charge up to 18volts for short periods of time to replenish low battery voltage or cope with high electrical loads"
I am not sure I believe this, is it true?