Ammeter behaviour and ignition light on questions

[dwomby]

My car has an alternator with an internal regulator fitted in place of the original dynamo and regulator. Recently, the ignition warning light has refused to go out. It glows a bit all the time. I read that is an indication that the charging system is not working and there being an imbalance between the voltage coming from the battery and that from the alternator.

I checked the battery - 12.6V when the engine was off. 14.4V when the engine was running. So, those seem to indicate battery and alternator are working. Then today, driving, I noticed in a short distance today (say 3miles) the ammeter read as follows (all readings are approximate)

Ignition on, engine not running 0A
Starter engaged -20A
Engine running at idle - +20A
Driving +20a then a sudden drop to 0A. A few minutes later it was back at +20A then it dropped to 0A again, then up to 15A and stayed there until the engine was turned off.

I don't have experience monitoring an ammeter but is that normal? I'd expect it to stay + charging and gradually drop to 0 as the battery became recharged not drop to 0 then jump back up.

Any insights into this behaviour and/or the dimly glowing ignition light would be appreciated. Thanks.

David