when i disconnect pos battery it dies why
Could be bad alternator,but some time,s it all depend,s on the vehicle,and it,s power accesorie,s,some will run with cable off but some will not,if you are having cranking problem,s go have alternator checked,and have the battery load tested.
T S T is right about having your charging system checked, but you should never ever remove a battery cable with the engine running, I have seen what damage that can do to the electronics on a vehicle. You could do that to the old generator systems as the output amperage was low at idle. But those days are gone.
Search Ford F-150 Questions
Ford F-150 Experts