Do these mount at the factory fog light location without drilling or modification?

Yes. These use factory mounting points and bolt in where the original fog lights were. No drilling or bracket fabrication needed.

Is the switch already wired to this assembly, or do I need to run my own harness?

The switch comes integrated with the assembly. Basic power and ground connections are all you'll need—no relay or complex wiring required.

Will these work with my factory bumper, or do I need a custom bumper to install them?

They're designed for the factory bumper opening. As long as your bumper has the stock fog light holes, these will fit. Test-fit before final assembly to confirm fitment on your specific vehicle.