you can either use the original alternator wiring, or use the one off the 20v. if you use the 20v one all you do is cut the 2/4 pin plug off near the starter and wire the original alt blue wire up to it. the mk1 has a spade plug near the battery live for the alternator. or you can splice the 20v mating plug onto the original blue wire, then it'll plug in near the starter. originally mk1/2 alternator main live is wired to the starter terminal, but mk4 on it goes straight to battery. either is fine
good question, I'm not even sure the 20v has one? thought it was only on the diesels. I have a diesel alt with clutch on my abf, but the only reason for that is the alternator was cheap