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

The assembly ships without a bulb—you'll transfer your existing bulb from the old headlight or source a replacement separately. Standard H11 or 9006 bulbs (depending on your trim level) fit the housing.

Will this bolt up to my existing wiring harness?

Yes. This assembly uses the factory connector at the back of the housing, so your OEM wiring harness plugs in without modification or adapters.

Do I need primer or paint before installing?

The housing is ready to bolt on as-is. If the black plastic finish shows wear after removal, you can touch it up with spray-on trim paint, but it's not required for function.