Does this require any wiring harness or relay kit?

The integrated switch handles the control circuit. You'll need to run power from your battery to the switch and ground the assembly—standard 12V automotive wiring. If you're not comfortable with electrical work, have a shop handle the power connection.

Will these mount at the factory fog light location?

Yes, these are designed for factory mounting points. No drilling or cutting required—bolt directly into the existing holes on your bumper.

Can I replace just the bulbs later?

H10 is a standard automotive bulb type. You can source replacements anywhere once the originals burn out. They twist out and in—no special tools needed.