Alright check it out. I posted in this in another forum and someone said I should post here. I have a 99 F-150 4x4 wih a 4.6 litre. 2 weeks ago the battery ligh came on on the dash while driving. I assumed the battery went bad as the heat in bakersfield destroys everything. I had to make a stop so I left the truck running while in went in the store, when I came out it was making a horrible noise. I jumped in drove home and starting listening. Come to find out it was the alternator. I thought maybe the battery being dead had some effect on it so I jerked the bat. out and bought a new one. Came home put it in and the noise continued. I went to Ford and bought a new alternator. Slammed it in and still had the prob. tested the battery and only 12 volts. Thought I had a bat alt. so I took it back and got another. Still didn't fix. Traced out the ground cable to the frame and starter which had some issues. I replaced it from top to bottom and still no Fix. I checked the #11 fuse and the #111 fuse and both are good. What else could it be and how do I check. I have a volt meter so I can test whatever, please advise as I am selling the truck and need to take care of asap.