Do these plug directly into the factory connectors, or do I need a wiring harness adapter?

These mount at factory connection points and work with the stock electrical connectors — no harness or adapter needed. Plug them in and secure them at the mounting bracket.

Will these work with the factory fog light switch, or do I need to wire them differently?

They're designed to work through your existing fog light switch. As long as the factory switch controls your fog circuit, these will respond to it without modification.

Are these street legal, or are they for off-road use only?

Fog lights are legal for street use when used appropriately in low-visibility conditions. These are clear lens units designed for standard fog light operation — use them like you would OEM fog lights.