Hi Sam. Are the Alternators Identical. ? I,E do they both have clutch pulleys or Standard Pulleys. ?

When you say that you fitted an Alternator and it appeared to cure it, How long has the new unit been fitted before the problem returned. ?

The Main way to tell the difference between the 2 types of alternator are, The Old Type -- ( usually up to about 2004 which fits the standard engine and some early common Rail versions, The Terminals should be Marked L and W. and is Usually but not always fitted with a standard pulley.

The Later Type Fitted around 2004 onwards is marked up L and F and is Usually fitted with a Clutch pulley.

If you buy a Chinese copy alternator or a Recon unit and it isn't marked up then you will struggle to see the difference.

H.T.H. Tony.