Okay, I have searched the forum and got some info on what to check, but just wanted to see what you guys would do.
My problems:
Drove the car and noticed low voltage - like 12.4-12.6 while driving with nothing really on. Then wouldn't start the next day.
Had the battery tested - bad cell in it, so I replaced it.
Tried again, same thing. So now I think its the alterantor (makes sense).
Replaced that with a brand new one last night and drove it. Still at 12.7 or so with lights on, but would go over 13 volts with more throttle. But basically too low in the 12.6-12.7 volt range.

So I have a new battery and alternator and still low volts. I did notice that the rear plate light is not working (put a new bulb in it too), and a whack to it made it kinda flash on for a brief second. Maybe something to this? Seems to be not working the same time as the low volts . . .

What and where should I check?