I have a 98 150 4.6L. Going to work one day the battery went dead so i'm thinking alternator. I took the alternator into napa they tested it and I had a good friend test it both are telling me its good. I bought a new battery, new drive belt, and a new voltage regulator for the alternator. It is still happening the battery will drain while i'm driving my lights will get dim and the truck won't run right and all of the sudden it kicks in and charges up again than it will drain again. I don't know what the problem is. Experts out there please lend a hand. Thanks!!

 

Might want to post this in the electrical section. Sounds like a bad ground or another connection. I would look for corrision of a wire that is damaged.