Do these use factory wiring or do I need a harness adapter?

These are direct OEM replacements, so they're designed to plug into your factory mirror connectors. If your vehicle has aftermarket wiring already modified, test the connectors before final installation.

Will the power adjustment and heating work immediately after installation?

Yes, once connected to your factory harness. If either feature doesn't activate, check that all connectors are fully seated and your vehicle's mirror control switch is in the proper position.

What's the return window if these don't fit or work as expected?

Contact ModSupply customer service with photos or a description of the issue. Returns follow standard policy — keep your original packaging in case you need to ship them back.