Does this come with wiring harness and connectors?

Assembly ships as the light unit only. Your existing third brake light wiring plugs directly into this unit — no rewiring needed if you're replacing OEM.

Will I need to remove the tailgate to install this?

Installation method depends on your truck's current setup. The light mounts at the factory location, but you may need to drop the tailgate for access — refer to your service manual for best approach on your year.

Does the black finish need prep before install, or is it ready to bolt on?

Ready to install out of the box. The black finish is factory-applied and does not require sanding, primer, or paint.