4.9 engine. Starter will not disengage after engine starts.
Fly wheel is new. Starter was new. Solenoid was new. Ground cable back to battery severely overheated.
Sounds as if the new starter may be defective, You may want to look at the starter relay...maybe hanging up..
Buy a quality rebuilt starter, most are crap. Get one where everything has been rebuilt, not just the defective parts.
From what I understand you purchased a flywheel and starter for a 30 year old vehicle. Do you still have the old parts? If so check and make sure the new pinion gear matches the new cogs in the flywheel. If not matched they will bind. Sounds like one or the other may be mismatched. Worth a check.
Looking for a Used F-150 in your area?
CarGurus has 10,393 nationwide F-150 listings starting at $2,995.
Search Ford F-150 Questions
Ford F-150 Experts