Yesterday I got in my 1999 f150 and it was completely dead. No lights would turn on. I took battery to Auto parts place and they said it was fine and charged Battery. Put Battery back in and it started. Few minutes later tried to start and would turn over but acted like it was not getting fuel or air. Checked air filter and had 3/4 tank. It started but notice when turned off idiot lights for oil pressure and service engine stayed on. Did not expect two lights to kill battery. But this Morning battery dead again. Charging now but what is causing the drain on battery in less that 12 hours? Do I have a short? Bad fuss? ??? Never had this issue before.

 

High likelyhood the alternator has a shorted diode stack or the integrated regulator is faulty.
A good sized spark when putting on the last cable is a good indicator.
A shorted stack provides a circuit to ground through the alternator. Another indicator is the alternator case may feel warm on a cold motor.
Good luck.

 

+1 on Alternator

 

Thanks Bluegrass7,

Alternator changed and battery and truck back to normal!!!