Do I need to drill or modify the bumper to install these?

These mount at factory fog light locations using existing mounting points — no drilling or bumper modification required. Standard hand tools and a socket set handle the job.

Will the switch work with my factory wiring, or do I need an external relay?

The switch comes with its own wiring harness and handles the circuit internally. You're connecting directly to the factory fog light harness if it exists, or running new power and ground to the battery.

Are replacement bulbs easy to source if one burns out?

Yes — H11 is a standard automotive bulb type available at any auto parts store, big-box retailer, or online. Cost is minimal and replacement takes minutes once the housing is in place.