Alternators bad.. Right?

[96Cruiser13]

My battery light has been on lately, and i got in the truck to start it this morning, and nothing. This is a new battery by the way. I jump started it with a friend, and it was fine for a second, then when i unhooked it from my friends truck, it bogged down and turned off.. The lights and radio work, but its like theres not enough juice for the car to run.
Any help is appreciated.
By the way, the alternator has been underwater before...

 

[96Cruiser13]

I've been working on the truck, and the connection to the alternator doesn't seem to be too sturdy, and does not have a wire cover. Is this typical?

 

[landtank]

I believe the battery light means the battery is discharging which usually points to the alternator. By underwater you mean a 3 day bath, correct? I'd jump the truck again and check voltage across the battery when the truck is running and the head lights on. You should see @14.2v if the alternator is putting out correctly.

 

[Red Beard]

Make sure your alternator fuse is still fused. Its in the underhood fusebox. A big 150A'r or something. If that blows your alt won't do anything for your battery.