Do these lights need any wiring or can I really just plug them in?

The switch comes wired into the kit, but you'll need to run the main harness from the lights to your battery or fuse box. It's a straightforward install if you're comfortable routing a cable and tapping into power — otherwise a shop can knock it out in under an hour.

Will these fit if my bumper is already damaged or modified?

These mount at factory rocker and bumper points. If your bumper is cracked or heavily modified, test-fit first. Slight adjustments to the mounting bracket can usually work around minor damage.

What if one light burns out — do I replace just the bulb or the whole unit?

The bulb is user-replaceable. You won't need to remove the entire light assembly — just access the bulb from behind the lens and swap it out.