2003 f-150 4.6 new battery, new alternator, new alt. plug pig tail. All fuses and fusible links good, Still not charging????

At idle whats your multimeter reading at the battery terminals? did you perform any voltage drop tests.

Check connections on the alternator for good contact and correctness. Use a multimeter to check the voltage at the battery with the engine running. Check the grounds. Hopefully you disconnected the battery prior to installing the new alternator. Alternators now contain electronic components. Reversing the polarity by mistake and harm the new alternator.