1999 Dodge Dakota battery/alternator

I just put and whole new clutch system in my truck and while it was sitting the battery died. I finished the job and charged the battery back up, it held a charge and I drove the truck for four days fine. Then I started to have to jump the truck off every time I wanted to start it. So I checked the charge on the battery and it was low so I charged it up and still had to jump it off the get it started. But with the truck off the battery read good. But with it on it only read 12.59 amp and it steadly drops until it finally will die. So I took off the alternator and had it tested and it passed. So I was told that there is a fuse in the line that plugs into the back of the alernator but I can't find it, and I don't know what else could be the problem. Could you tell me if you know the problem. Thanks billy