so im trying to restore headlamps on 99 accord, they are plastic

-first i will wetsand up to 2000 grit
-but what product of polish should i use to buff with?
-finally what product to seal everything with. i have heard some type of uv sealant/protector so that the yellow/fog look does not come back?

 

This might help:

Most auto parts stores have a kit for polishing head and taillight lenses. Brands typically found at your local auto parts or big box store include:
◊ Meguiar's PlastX

◊ Novus (#2 for fine scratches, #3 for polish)

◊ Mothers Plastic Polish

◊ DuPont polishing compound (white)

◊ Brasso (the manufacturer says it’s for polishing metal, but people often use it for polishing plastic, including CDs and DVDs as well as iPod screens).
◊ Gel fluoride toothpaste*
◊ Brake part/carb/throttle body cleaner**

Compound Application techniques.
Rub on just using a regular terry cloth towel. Some people just grab an old gym sock. One CarSpace member used very fine polishing compound and a soft cotton buffing pad on a drill motor. Be careful or you will put burn marks in the plastic and they are almost impossible to get out.
Whether you use a polishing compound, toothpaste, Brasso or one of the commercial plastic polishes to clear up the haze, the technique is largely the same. Just put some on a small cloth and use it as if you were using a very fine rubbing compound, turning the cloth as needed and re-wetting with the polish, then finishing with a clean, dry cloth. Repeat until any haze, scratches, and pitting disappear. These products generally are very fine abrasives, not just cleaners, so they actually grind out the scratches and pits, with a little bit of effort.
*The suggested use of fluoride toothpaste was from a boat yard repair that a CarSpace member had success with. Smear some gel fluoride toothpaste on the lenses and rub it on with your fingers and leave it on overnight. Then simply wash it off. The fluoride supposedly reacts with the acrylic to remove the UV aged film, but maybe it’s just the abrasive nature of the toothpaste that actually does the work. Chances are you have some toothpaste handy you can try and save yourself a trip to the store.
** See Doohickey's comment and photos below for his throttle body cleaner trick - thanks Doohickey!
Buffing.
Some people use a series of fine grit sandpaper to wet sand the lenses, but that may be a bit extreme unless you can’t get satisfactory results with the polishing techniques above.

To buff out headlight lenses, it's best (but not nessasary) to remove the light assembly first. Then start with 600 or 800 grit wet/dry paper and work your way up to 1200, and finally 2000 grit. Let the paper do the work and don't use too much elbow grease. Keep a spray bottle of water handy and spritz your work frequently. Then polish as above. You can easily make a huge improvement with the investment of a few hours of your time and a few bucks worth of supplies.

P

 

I usually wetsand the first time, then use Mother's Mag and Aluminum Polish. After the first time, it should just need the polish. Even though it's for metal, it works REALLY well on plastic! If you search around, a lot of people use it.

 

I've heard of the mag polish working but never tried it.

on one of my cars the headlights were badly yellowed and the clear coat/protection was worn off as well.

I think I started out with 600 wet, then went to 1000 wet, then 1500 wet and finally 2000 wet. Used the 600 to remove all the yellow/peeling clear coat, then each step I made sure the scratches from the sandpaper were getting finer and finer.

I decided to leave the headlights on the car to hold them in place. I had the bumper removed with I was running oil lines so I didn't worry about scratching that and I just put some painters tape over the fenders to protect from scratching with the sandpaper.

After sanding I used a 2 step cleaner/polish by 3M. the first one, the cleaner, is a bit more abrasive to help remove any larger scratches. The lens looked pretty good after that but I continued with the final which is much more of just a polish. That left the lens nice and smooth and crystal clear.

I went from a yellowed headlight that decreased my light output to a new looking headlight for the cost of some sandpaper and polish.

I never coated them after though. Couldn't make up my mind on what to use. I heard acrylic clear coat is good from some people but others say it's hard to make it look good so I didn't use anything. After I wash the car I just use some Meguiars PlastX and that removes the small scratches and buffs the lens up nicely.

I think I took some before and after pictures, I'll see if I can find them. My neighbor was really surprised how new looking they came out.

I'd be interested in hearing what some people have used to protect the lens.