Mine were pretty hazed, but it was only external, the insides cleaned up well. (The light holders were in good condition too.) So after replacing the gaskets and repairing the wiring, I only had to attend to the lenses.
Pan of water and 1000 grit wet dry with a rubber back pad. Use a lot of water to keep the paper from loading up. Sand in on direction only (thanks YouTube) until the lenses look uniform and "better". By this I mean when they dry they will be a little hazed. Hit them again with 2000 grit sand paper under water (or very wet). Rinse and dry completely.
I put on 3 coats of the Rustoleum Clear Coat 2X over about an hour, it was cold here so the drying time was not great. I noticed in the photos a little orange peel. That can be addressed later with 2000 grit or rubbing compound. (But I have a bunch of other stuff before that...)