Ever since I had the keyboard on my MacBook Pro replaced the back light has not worked. Occasionally I’ve looked into it (usually when I find myself in low light conditions and become annoyed that it’s not working) and haven’t found anything that worked for me.

Some of the suggestions I’ve found in the various forums have included:
- Pressing F8, F9, F10.
- Covering the light sensor behind the speakers to get the F8 key to work in lighted conditions.
- Installing Lab Tick to manually control the back lighting.

None of these suggestions worked in my case, and since there were usually a few other people who tried these solutions without success I just accepted it and went on with my work (and assumed the technicians had replaced my keyboard with the “cheap” version).

Yesterday while I was typing in low-light conditions, I occasionally noticed the back light flickering on. I experimented a little and realized it was happening when I happened to press a key with above-average force. So, using both hands I gently, but firmly pressed down on the entire keyboard and voila- my back light started working again. It’s only been a day, but I haven’t had a problem since.

Since my keyboard has functioned flawlessly aside from the back light, I assume the back light has a separate connector. So if you find that the “standard” solutions don’t work for you, making sure your keyboard is completely connected *might work.

* It’s also possible that your keyboard is broken.