Will this use my factory wiring or do I need to run new harnesses?

The switch integrates at your factory dash location, so you're not running additional engine bay wiring. Test-fit the switch bezel before final installation to confirm a clean fit with your interior trim.

What if the bulb burns out—can I replace it myself?

Yes. The H11 bulb is the standard replacement part for these housings. You can source replacements anywhere automotive bulbs are sold.

Do I need to paint or prep these before installing?

The clear lens is ready to mount as-is. The housings are pre-finished, so no paint or primer work is needed on your end.