Do I need to rewire this to my brake light circuit?

Depends on whether your hatch has a dedicated third brake light wire already run. If your original third light was wired in, you can tap directly into that. If not, you'll need to run a new line from your brake switch or tail light harness.

Will this work with my factory wiring harness?

The assembly is designed for direct bolt-in fit at factory mounting points. Wire connector type and pin configuration are not specified — test-fit and verify compatibility with your existing harness before final installation.

Can I return this if it doesn't fit once I open it?

Contact ModSupply customer service with photos of the fitment issue. They'll walk you through a return or exchange if the unit doesn't align properly with your factory location.