Do these mount at factory fog light locations without drilling or brackets?

Yes. These are designed for factory mounting points — no drilling, no custom brackets. The bezel clips into the OEM openings.

Does the wiring harness connect to the existing car switch or do I need to run a separate one?

This kit includes its own switch. You'll wire it into your existing fog light circuit if one exists, or run it as a standalone switch. Consult your vehicle's wiring diagram or a local installer if you're unsure about circuit integration.

Are the bulbs replaceable if one burns out later?

Yes. H11 is a standard bulb type — any auto parts store carries replacements. Pop the assembly and swap it out.