How to fix no backlit keyboard on BootCamp Windows 8 partition
Keyboard lights work perfectly in both W7 and W8. (and Fn F5 and Fn F6 control the intensity)

Try reinstalling the WindowsSupport files (which reinstalls the keyboard driver), you should not lose T++ functionality, but if you do just reinstall it (Power Plan Assist reinstallation is not needed) 

Sometimes after some sleep-wake cycles the dimmer function stops working (Pressing Fn F5-F6 brings up a gray panel with a disabled sign), rebooting fixes the problem.