what does cause yellowed back up lenses ?

[Nacho-RT74]

what you read...

I want to try keep mines best as posible along the years. They are NOS ( well at least when I found and install them 4 years ago LOL )

[Just 6T9 CHGR]

Sunlight & ozone yellows plastic over time.  Unless you keep your car out of the sun and the elements, eventually you probably will have yellow reverse lights.

Although now, plastics are designed to withstand the elements.

If you can reproduce them with todays plastic technology you'll be OK

[dd44068]

Not sure if this will work but try some compound and a buffer or a lot of handwork. I was told this works.

[JimsSE]

I agree with both Just 6T9_CHGR.... and dd44068.

My suggestion is to start off with keeping a good coat of UV protectant wax on them.  That should keep them looking good for a long time. 

Then, if time and sunlight still start turning them yellow (like mine were), I'd use some polishing compund (watered down) and a cleaner/wax combination.

I've taken a set of extremely yellow turn signal and back-up light lenses and started off with 220 grit sand paper wet, then 1000 grit wet, then polishing compound, and then finally Meguires polisher/wax.  You have to do this multiple times depending on how yellow they are but you'll be amazed at the outcome.

Bottom line - use the lightest stuff possible to clear them up.  If that doesn't work move up to the next step in agressiveness, and so on.

A word of caution...  Some chemicals will react with the plastic.  I bought some 3M stuff specifically for clear lens scratches but I swear that's what put "milky" spider lines in the lens.

There's my $.02.

Jim

   

[Silver R/T]

try some GS-27 on them