Alfetta GTV 2.0 - Alternator warning light

[fack33]

The alternator warning light on my GTV 2.0 operates normally when the engine is running but comes on and stays on when the engine stops even with the keys in my pocket. The (6 month old) battery goes flat overnight. The fact the light goes off when the engine is running means this doesn't seem to quite fit the alternator brushes type problem. Any ideas out there?
Thanks

[Neil Choi]

I suspect the diode pack in the alternator has died and hence battery leaks current out and goes flat overnight as you mentioned.  Either have the diode replaced or another alternator.  These alternators are getting on, 30 years old, so the replacement could be faulty or going to failed at some stage too if not rebuilt or a new one which could be pricey.  You can go for a small Nippon Denso one too.