Tool for making clean ground connections

I have seen star washers, I have seen U clips that have piercing points.

I agree with 67dart273 that our old cars were less than steller in the grounding department. But they also have mostly survived for 50+ years.

I ABSOLUTLY agree the there is no reason to scrape paint off and I would never do it.

As for bolt or screw threads creating a ground path, they absolutely do. Most if not all, screws onto sheet metal were punched holes that left a flange and a smaller ID hole than the screw OD. The screw cuts the threads and absolutely is metal to metal.

Just like if you put a reasonable amount of Teflon tape on a sensor and screw it in it makes metal to metal contact.