How do I determine if its
the
alt. or the regulator.

With a progressive test light or (better yet) a meter.

With the engine running, measure the voltage at the connections on the back of
the alternator. Should be well over 14 volts.
If it isn't, (and especially if its the same reading you're getting off your
battery terminals when the engine is not running or there is no charger
connected),
look at the alternator.