Does this switch come with the wiring harness, or do I need to source that separately?

Switch assembly only — no harness included. Your vehicle's existing fog light harness plugs directly into the connector on this switch.

Will this work if my original switch is broken but my fog lights still function?

Yes. If your bulbs and wiring are good, this switch restores control. Test your lights before installation to confirm the harness is live.

Do I need any tools or fasteners beyond what's in the box?

You'll need a panel removal tool or flathead screwdriver to pop the switch pocket from the dash. The switch itself uses factory clips — no additional hardware required.