electrical problem?

[FAT TONY]

Alright so i drove to school one day and forgot to turn off the light. so for about six hours the light were on and drained the battery

I got a boost from a friend and was able to make it home but when i made it home i noticed my voltage was low on the gauge it was putting out about ten volts, so i decided to turn the truck off and turn it back on but when i did that the battery was to low to restart the truck. figured it was the alternator so i went to have it checked and it passed so then i figured voltage regulator but when i got a new one it didnt fix the problem. so now im kind of clueless as to what it could be.

when the truck is running i disconnect the ground wire and it turns off so i know its something in the alternator but what could it be?, the people at the auto parts store tested it about four times on the machine and it passed all four times, so if any one could help me out here it would be appreciated