Charging problems!! Please help :(
 

So... i have a 2005 Cobalt SS 2.0L LSJ turbo SWAPPED..and i have been without the car for about a month now.. For some unknown reason, my car wont charge my battery. I hopped in the car and drove down the street and the battery light comes on and chimes, after driving for about 20 mins to a half hour on a full charge, the electric starts to dim and the car shuts off. The fuel pump is the last thing to shut off.. I just changed the alternator twice and battery twice, checked all grounds and wiring. I even disconnected the new lights i just installed because i thought that may be the cause. Any ideas what it could possibly be? I ran the computer and it says there are no codes.. im currently searching a wiring diagram for the computer to see if the wire from the computer to the alternator is making a connection or not... I checked the connector connecting to the alternator (possible voltage regulator) and it does not light up car running or not.. PLEASE help me get my car back :( ANY IDEAS???