98 Ford F150 4.2L, My head lights were diming, voltage needle moving alot, had the alternator replaced and new battery, still the same thing happening, Battery light still coming on, voltage needle still moving. any thoughts would the problem could be.

 

A problem past the battery and charge circuit.
You would have saved money by testing first to see that the charge system was functioning ok.
Can be an intermittant ground, short to ground, cross, headlite switch etc., anything with power to the truck's operating systems.