Will I need to drill or modify the bumper to install these?

These mount at the factory fog light positions—no drilling or cutting required. Line up the assembly with the existing openings and bolt down.

Does the switch work with the existing electrical system?

Yes. The harness taps into factory wiring points, and the switch mounts into the dash cavity where your Yaris expects it. No rewiring of the main harness needed.

What if I need to replace the bulb later?

H16 is a common bulb size and widely available at any auto parts store or online retailer. The socket design is standard, so any H16 replacement will fit.