I pinned this idea and decided to give it a try this weekend. All you need is a tube of plain ol'toothpaste (nothing fancy like gels) and some rags.
This is Chuck's truck and it is weird that only the passenger side headlight had this build up of grime and yuck. The other side was perfectly clear. Anyway this is the before.
I put a large around of the toothpaste on an old washcloth and then rubbed it over the light. It reminded me of waxing a car. I then used a clean towel and buffed the toothpaste off. While I was doing it Chuck came out and he was surprised how well this was working. He decided that we should do it a second time and the results were even better!
I will note that as a precaution we did drive the truck through the car wash when we were done. Chuck had a concern about any toothpaste we missed on the paint and chrome. He wasn't sure it it would have a negative effect over time. He tends to be on the cautious side.
We were both amazed by the transformation.