Thanks for replies.
Don't know about bad diode/ stator winding, Tim. Will take Alt to shop
to bench test.
Engine is Mercruiser MCM260. S/N is 6678458. Alt says Arco #60109
(marine SAE J1171)
Also says made by Mando on back. 55A.

At idle it was putting out 40A which Alternator shop guy said was
normal

I do have rust on main pulley, not on Alt tho. There's one culprit...

....couple questions from the Stupid ? Dept.
-- How do I find if I have 'bad engine ground'...?
-- How do I Iocate it and check to see if the fuse between battery and
alternator is good?

STB