Mine were out when I bought my 2007 CX9 used. I just replaced the bulb.
I imagine the filament in the bulb might be broken, and when you tap it, it reconnects it. (temporarily). Perhaps a new bulb is all that is required.
It's pretty easy to do; with the handle off the shifter (may not even be required), just pry the black plate upward. Don't pry the silver plate ON the black plate... that's not where the release is.