I am not sure, but my Ford Taurus is doing the same thing. I found that if I take the positive battery cable off for about 10 minutes and put it back on, they will work for about 2 weeks.
I found on my wife's 2001 Mercury Sable that the black connector going to the instrument cluster was loose. I cleaned the connections with electrical cleaner and reinstalled the cluster. It seems to solved the problem. The dash lights are L.E.D.'s and when I was removing the cluster I performed the Ford Wiggle test and the lights came on.
A sharp rap with the palm of your hand on the dash just forward of the steering wheel will light it up every time. Repeat when needed