When my MK2 is idling the charging system dashlight is on. Sometimes when I come to a stop and it will take a second but it will come on then I'll drive off and it goes away. The regulator is newish and showed some corrosion so i cleaned that off god and put dielectric bulb grease on it didn't change anything..
a glowing light at idle is normal(at night), take a multi-meter and check charge voltage at idle.
if light is brighter than glowing check battery, connections/cables(and grounds), check voltage of battery, key off, and voltage at idle and at higher revs(around 2000rpm). check voltage drop and at grounds too.
could be a faulty regulator.?
Does it still do it with your headlights on,.. with a load?
less bright and the brights even less.
When my alt light flickers at idle it only takes a small load, like opening the door or touching the brakes to make it go out.
The exciter wire female spade terminal was about disconnected from the exciter wire 1 or 2 braids still making contact with the spade coupled with a super rusty D+ terminal on the alt new female space cleaned of the rust and some di electric grease and its good to go no more dim light.
I have a dim light with perfect connections.. only with no load on the alt though.