2001 Marquis having alternator problems

My 2001 Grand Marquis recently stopped and would not start again. After some diagnostics
I determined that the alternator wasn't charging properly and replaced it. A week later the
new alternator wasn't working and we replaced that one as well under warranty - it was
bench tested three times, passed once and failed twice. Each time the alternator was
replaced a volt meter showed the alternator was charging just fine 13.7 - 14.2 range.

Now two weeks later, and the other night I had the car's voltage meter show no charge, the
lights dimmed and the ABS and Traction control lights came on. When I got home I trickle
charged the battery as it was close to dead ( this is a 9 month old battery). I have checked
both connections and traced back the wiring they seem to be fine. I have replaced positive
and negative battery connections and traced back those wires, they also appear to be fine.
What am I missing here? The serpentine belt is less than a year old and the tensioner
seems to be working properly with no excess slack. Any ideas??