[Trisman]

I went through this only the other week...

If you plan to replace the complete alternator, either type will fit the diesel engined cars. So it makes sense to fit a later, higher output alternator.

So, the later two pin or the earlier three pin alternators will fit & work, regardless of whether or not your car's wiring loom has a two or three pin plug.

Replacing a complete alternator is apparently a bear of a job...

I decided to replace just the regulator, without taking the alternator off the car.

It's is a fiddly job, but as I mentioned, is apparently a lot quicker & easier than removing & replacing the alternator.

It took me around 3/4 of an hour on a cold day. The only difficult bit (part from keeping my hands warm!) was removing the gloop the manufacturers see fit to smear on the two small connectors. (See the first picture above in Colvert's post).

The regulators are not interchangeable. You have to get a three pin one for the earlier, three pin alternators, or a two pin one for the later two pin ones.

In my case, I did what DMGRS suggested & obtained both types of regulator. Turned out that my first purchase (a three pin regulator) was correct & I didn't even need to take the later two-pin type out of it's box! It was sent back for a (pre-agreed) refund.