Do these plug into the factory wiring or do I need to splice into the harness?

These are designed to work with the existing fog light mounting points on your tC. Test-fit the connectors first — if they don't align with your factory loom, you may need to adapt or extend the harness depending on prior bumper work.

Are the lenses sealed against water intrusion?

Standard fog light construction includes sealed housing, but condensation can still form if there's a temperature swing. If fogging develops inside the lens, drill a small drain hole at the bottom of the housing or run a heat gun to dry it out.

Can I use different bulbs, like LED or a higher-wattage H11?

H11 is the standard socket for these assemblies. LED replacements fit the same socket, but verify your vehicle's electrical system handles the lower draw before installing — some older wiring may trigger a dash warning. Stick with OEM wattage or contact your vehicle manual for safe substitutes.