Do I need to run new wire through the firewall?

No. The switch harness integrates into this assembly, so routing is handled at the bumper and dash level — cleaner install than patching into existing circuits.

Will this assembly fit without modifying my bumper or frame?

These mount at factory points, so no drilling or bracket work. Do a test fit before final installation to confirm alignment with your bumper opening.

What if a bulb burns out — can I replace it easily?

Bulb access and replacement method depend on your specific vehicle. Check your service manual or test-fit the assembly to see how the lens sits in relation to your bumper.