Will this plug directly into the factory harness?

Yes. This is an OEM replacement unit designed for direct installation into the existing factory connector and mounting points.

Do I need to replace the bulb, or does it come pre-installed?

The bulb is not included with this assembly. You'll need to source the correct bulb type for your model year and install it before mounting the light.

Can I install this myself with basic hand tools?

Installation is straightforward for anyone comfortable removing a trim panel and disconnecting a factory connector. You'll need basic hand tools and a replacement bulb.