Dell Laptop Keyboard Illumination

I bought a refurbished Dell 7420e laptop to replace my aging Dell The 7470 has an S key that works irregularly. Dell laptops have a “backlight”, and the letters on the black-body of the keys can glow under the right circumstances. Very handy when positioning your fingers on the keyboard when in dim rooms. After installing Arch Linux, the 7420e keyboard would not illuminate. The keyboard backlight worked, the POST flashed it during reboots.