Will these work with my factory wiring harness?

These mount at factory connection points and are designed as a direct swap. Your existing Sierra harness should connect without modification, but test-fit before final installation to confirm alignment.

Do I need to buy HID bulbs separately?

Yes. These housings are HID-ready but don't come with bulbs installed. You'll source HID bulbs that match your preferred color temperature separately.

What if they don't line up when I install them?

Aim adjustment is standard on most headlight housings—small vertical and horizontal screws behind the assembly. If alignment is still off after adjustment, contact support with photos before committing to any permanent modifications.