Do these use the factory wiring harness?

These mount at the factory fog light locations, so you'll use your vehicle's existing wiring if fog lights were originally equipped. If your Mustang didn't come with fogs, you'll need to source or run a separate harness and switch.

Will I need any brackets or hardware to install these?

Installation hardware for mounting is not confirmed in the specs. Test-fit the assemblies at the factory mounting points before committing to fasteners—you may need clips, brackets, or fasteners depending on your Mustang's trim level and original configuration.

Are the lenses sealed or can moisture get inside?

The clear lens construction is not detailed in the product specs. Inspect the seal around the lens perimeter before installation; if condensation appears after mounting, verify the gasket is seated fully or apply weatherproof sealant around the base.