Will this plug directly into my existing wiring, or do I need an adapter?

The OEM connector matches factory wiring harnesses on compatible 4-door Civics. If your vehicle originally came with powered folding mirrors, this assembly will plug in without modification. If your car has manual mirrors, you'll need to evaluate your vehicle's electrical setup before installation.

Is this the complete mirror assembly, or just the housing?

This is the complete assembly — glass, backing plate, motor, and all internal components are included. It's ready to bolt on and connect.

What's the return process if the mirror doesn't work after installation?

Test the assembly before final installation by connecting it to power and checking fold/unfold function. Contact ModSupply support with photos and a description of the issue if problems arise — most electrical or mechanical failures are eligible for replacement.