If it is a plastic cover, I use Mcguires PlastiK . It took the yellow tinge off a set of plastic lenses on a 1995 ford Crown Victoria and made them just like new. After using this I seal the surface with Mcguires mirror polish. I also saw PlastiX which also works. It's by Mcguires also.
Hope this helps. Joe
99 F-350 4X4 PSD pulling a 24' Nash travel trailer