Do I need any extra fasteners or hardware to install these?

The motor and regulator mount to existing door anchor points. Verify your door panels have all factory mounting holes intact before installation — if hardware is missing or stripped, you'll need to source replacement bolts to match your door's fastening points.

Can I install just one side, or do I have to buy both?

This set includes both driver and passenger assemblies. You can install one side now and save the other for later, but the set doesn't break up — you're purchasing the pair together.

Will these work if my existing wiring harness is damaged?

These motors plug into your factory harness. If wires are corroded or broken, the motor won't function — inspect the harness connector inside the door before installation to avoid a failed swap.