Do these bolt into the factory fog light openings?

Yes—these are designed for the factory locations on your Sequoia. No cutting or drilling required; mounting uses existing points.

Will I need to run new wiring, or can I tap into existing harnesses?

These come with their own switch and harness. You'll need to run power to the battery and ground to a solid chassis point. Wiring complexity depends on your comfort level; a basic understanding of automotive electrical is helpful.

Can I replace just one side, or do they have to be installed as a pair?

Installation as a pair is recommended for balanced appearance and even light coverage. Running mismatched fogs will look incomplete up front.