Will this plug directly into my Civic's electrical connector?

Yes—this is engineered as a direct OEM replacement, so it connects to your factory wiring harness without modification. Just align the mounting points and secure.

Do I need any additional hardware to install this mirror?

Mounting hardware is not included with this assembly. Use your original fasteners or refer to your service manual for the correct torque spec and bolt sizing.

What if the power function doesn't work right after install?

Check that the connector is fully seated in the door harness and that power is reaching the mirror. If the electrical connection is solid and the mirror still doesn't adjust, the unit may need evaluation.