Just do the bloody simple thing and disconnect the blue wire with the ignition on, does the light go OFF, if it does then put multimetre on battery, not voltage start engine still with blue wire off, note reading now touch a LIVE onto the terminal from where the blue wire came, should be marked IND.
AS the live is touched on the alternator IND terminal the voltage should rise as it starts charging, you don't need to hold it there just a good positive touch is all it needs.
This LIVE touch it normally gets through the blue wire coming from the charge light, the IND terminal when it is charging turns Positive this then puts out charging light, as two positives won't make a light glow.
It is entirely possible for a new alt to be faulty, it is also entirely possible for a alt to be charging perfectly REGARDLESS of the light being on or off too.
tabetha