1996 dodge grand caravan alternator

I have a 1996 Grand caravan 3.3 liter, After driving the van around town for about 20-30 min I get the battery light on. Before I drove the van I checked the voltage out put it was 14.2vdc with engine at idle. When I got the battery light I pulled over and checked the out put it was reading 8.0vdc. How can I check to see if it is the voltage regulator or if its just the generator? I had just replaced the generator with a brand new one 3 months ago from the dealer at that time it was doing about the same thing. I pulled the alternator out and bench tested it and it passed with no problems. Im still questioning that when the alternator gets hot it gets an open in the fielding. Any suggestions would be helpful.

So I finally found a used alternator (the only other alternator was in Denver Colorado) in a local junkyard, So I bench tested it, and passed. I Installed the alternator and found no further problems.

I also contacted the local dealership they can test the Power control module to see if the voltage regulator is working or not. For a starter fee of $40.