Is it the Alt. or Volt. Reg. ?

Need some help on charging issues. Coming home last night from the White House after HBO filming with the 65 Valiant I noticed the Amp meter on discharge. Put my meter on the battery when I got home and sure enough, not charging. I've upgraded to the elect. volt. reg. a few years ago and new alternator at that same time. What are the test procedures to determine whether it's a bad voltage regulator or a bad alternator? Thanks.