comments:
Ground is about good contact. Rust is bad but doesn't guarantee hindered contact. What I would do is just remove the screw. Check the hole for rust. If it's good, move on. If not. Maybe buy a small tap and die set to remove the grime. OR find another connection point. Do some research on installing audio equipment. But the goal is removing all rust you can. That's it. You can spread the connector apart and take it off. Once off. Check the wire underneath. If it's rusted you need to trim it or replace it. Trimming is ideal but doesn't work if there's no slack. You can do it. This is simple. Your second picture should work just fine. Rust doesn't form on some medals. This tells me they didn't use a quality connector. The second picture you showed is for the cars battery. You can't screw it down. I'll find a link. https://a.co/d/04kaXeew That's close to what you need