I just had the situation where a faulty voltage regulator prevented the alternator from charging the battery. That problem was solved with a new regulator; but what needs fixing now is that the charge indicator lamp never came on, even though battery voltage became so low that the car couldn't run. With some warning, I could have dealt with this fault before my wife got stranded!
I need some help here: 1) what is the threshold point at which the lamp should be turned on? 2) what is the best way to test that it's truly operating at the threshold? and 3) if need be, how can the threshold point be changed to give an earlier warning?
The lamp does illuminate on ignition as it should.

Thanks,
Barrie