Some preliminary "quick checks"
Turn key to "run" engine off
Use a test light or meter. Probe the blue field wire down at the alernator, should be same as battery voltage.
Come up an yank connector off the regulator, probe both connector pins. Both should be 12V
Start car. Use a probe/ clip lead/ screwdriver to ground the GREEN wire at the regulator connector. See if you show a charge
If yes, replace regulator.
IF not
Go to alternator, unhook green field wire, and clip alternator field terminal to ground. Recheck the blue wire, you should still have 12V. See if it charges.
IF not, put your light / meter on the alternator "big" output stud. See if you get a nice bright light, increasing with RPM, or increasing voltage on your meter
IF not, troubles in the alternator
It gets much much deeper than this, so post back results