Does this mirror connect to the factory wiring harness?

Yes. This is an OEM assembly, so it uses the factory connector and harness points on your Fit. You plug it in where the old mirror harness connected — no splicing or adapter needed.

Will the heated function work right away after installation?

It should. The heat element is built into the glass. Once wired and powered, activate heat through your dashboard controls the same way you would in a stock Fit.

What if the signal bulb burns out later?

The signal housing is part of the assembly. You'll need to access the bulb from behind the mirror or replace the entire housing if the bulb socket fails — check your service manual for the exact bulb type and access point for your model year.