Strange alternator warning light - knackered alternator?

Hi all. At the end of a 900 mile holiday trip, the old girl developed an odd fault - as we stopped at a garage 1/2 mile away. Turned the key off, engine stopped and the alternator light came on - with the key out. Drove home and the problem disappeared, but the light came on again last night and is now permanently on. Turning the key to position 2 (normally alt and oil lights on) makes the light go out. Disconnecting the alternator at the plug makes the light go out, so the wiring isn't duff. The only solution I can see is a faulty diode pack - unless you know different? The alternator will have worked hard on the last 250 mile leg yesterday - full lights, wipers, trailer lights, stereo all on.

Diode pack has gone I suspect - if the bearings and things feel smooth enough you could put a new regulator in.

A good guess, but luckily for me the problem was due to poor construction - see the piccy. This is a RTX copy alternator, just over a year old. The quality of soldering leaves something to be desired! The rest of the joints were solid, but ugly.