I drove 2 hrs one way to purchase a f-150 that “only needed a starter” the price was right so I took a starter with me along with a brand new fully charged battery. Put the starter and battery in and on it. Tried to start but the pickup turned over very slowly and maybe never made a whole revolution and locked up. Tried again. Same thing. Is the 4.2 locked up on this pickup? I think so.

 

Remove the serpentine belt and try to start it. Problem may be an accessory.

If it still doesn't start, disconnect the battery and try to turn the engine manually.

If it won't turn manually you will know it is locked up.

 

What do you mean by lockup?
Did it just stop turning, you don't mean the engine seized do you? As you said you tried again and it did the same thing.......locked up.
Do you mean it stopped turning over? Not locked up?
Did you check the ground wire?
And how do the other starter to battery wires look?
Check with a Multireader?

 

Make sure your ground is solid…especially on the vehicle end.