Go to the Eastwood website and look. They have special polishing wheels and compounds for plastic. Makes it look like new if it is not trashed to start with. If the plastic is in decent shape, I have used Simichrome or similar polish on an old cotton towel with success.
Howard
When I installed the Cougar taillights on my Shelby clone, they had faint marks where the Cougar grilles were. I spent a bit of time with the Mother's wheel polish and they came right out. I wouldn't want to use it on clear plastic, like race car windows, but it did the trick for my red lenses.
Meguiars makes a plastic cleaner/polish system the does wonders on clear plastic. I used to use it on my motorcycle windshields with fantastic results. I sand most things with 1000-1500 grit and then use a buffing wheel with rouge on it. I then use the Meguiars as a finishing touch for that really shiny gloss look. I have even resurrected sets of yellowed headlight lenses this way.
Yup. Here is what toothpaste and a little bit to elbow grease can do. Both lights were in the same condition. Just toothpaste on a wet rag and start rubbing.