I have a 99 yamaha warrior it has the white plastic on it and it is faded and brown what is the best way to clean up the plastic and get it back to white sounds gay i know but my brother in law is harpin on me to clean it

 

use one of those magic eraser things. they do wonders for atv plastics.

 

Try some stuff called simple green. Its and all purpose cleaner you can get at a grocery or autoparts store

 

I use pledge to protect the plastic once it is clean. It also makes it easier to clean off the mud.

 

Maxima SC1 silicone spray, stuff is absolutely amazing, 7-9$ can depending upon where and how much you buy.

 

Depending on how scratched and embedded the dirt is, you might try scrubbing it with some Clorox clean-up...it will take off any remaining shine your plastic has, but it sounds like it's pretty toasted anyway.