...i got lucky! instead of a alternator or rectifier failure, they (morgan dealer) found out it was a connection cable and plug between those two. it was tie wrapped to the mainframe. result after 7300km of vibrations was disconnection and material death of these cable and plug.
so folks: take a look underneath your m3w and cut out all the tie wrapps. let hang the cabels a little loose for compensating all the bone shattering vibrations!!!
i did this. took me 15min. easy to do. great impact!