Will this plug directly into my factory wiring harness?

Yes. This is an OEM assembly with factory connector configuration. It matches your vehicle's original electrical harness without adapter or modification.

Does the heating element come on automatically or do I control it manually?

That depends on your vehicle's climate control setup. Some models integrate mirror heating into the rear-window defrost button; others have a dedicated switch. Your factory wiring determines activation method.

What if the BSD function doesn't activate after installation?

BSD capability is built into the mirror, but activation requires factory-compatible body control module programming. If the warning light doesn't illuminate, have your dealer scan the vehicle for any module conflicts or recalibration needs.