Sorry for replying to a very old post but I often use this site for help and don't like leaving crap info on it.
It took me a very long time to realise but yes that blue wire was important: It's the feed to the charging warning light and must help the voltage regulator work properly. The starter motor that came out obviously linked into the charging light circuit and there was a connector tied back near the battery terminal that I didn't pay enough attention to.
Never had any trouble with charging while they weren't linked up properly but often had slow wipers and heater motor. Idiot - didn't have email notification set up so never read rubjonny reply :embarassed:.
Guess that 8v harnesses were spec'd to take different standards of starter motors. All I had to do was join the two connectors with blue wires and all was back to perfect VW normal; it would be better if the wire was a little longer though.
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