I have a 2006 f250 w/6.0, batteries are dying. I have dissconected the cables and load checked batts. both are good, reconected pos cables put test light inline w/neg cable bright light checked w/meter 12.56v pulled all fuses 1by1 light stayed on disconected small red wire from driver side pos cable light went off. any ideas what it could be? Thanks for any help im lost...

 

I have a 2005 and mine is currently doing the exact same thing so right now I have a huge boat anchor but mines goin in the shop Thursday bcuz I've tried everything I can think of mine even has a new alternator so if u figure anything out please let me know otherwise I will let u know what the shop says on Thursday.

 

Quik update I narrowed it down to one connector on the back of the fuse panel inside the cab now just need to find a connector diag. to see where they go. I will update more later.

 

Update Some things just where not lining up so I put everthing back together and started over with load checking batt. What I found was when the batts where charged and hot 12.80+ volts they load check good, after they set disconected overnight both batts had 12.50+ volts but 1 batt load checked bad. I replaced the bad batt truck started great this morning. The batts where only 1 year old. I hate admitting that i screwed up and chased my tail on this but I hope this helps someone save some time and money. So try charging batts, then load check, then disconecting overnight then recheck. hope this helps