I have an 03 F-250 6.0. Had to jump it to get it started Saturday so I took it and had the alt and battries tested. All checked out good and started just fine. Last night was running into town and lost all my lights and finally the truck shut down. I'm at a loss on what else could affect the charging system. Any ideas??????

 

Are both batteries the same type and age? One battery might be dead and sucking the life out of the other one.

Bad ground?

How old are batteries?

Where did you get alt and batteries tested? I know lots of parts stores test them but there are many store employees that don't know how to test them right.

 

I'd take it to an automotive electric specialty shop to have the alternator tested. Sounds like it isn't putting out, which means you are running your electric load off batteries only. Once they are drained, lights dim and truck no go no mo.

 

Both battries were replaced in March with Interstates. Ford just called and it was the alternator. Gotta love your local parts store.