I had to refer to this thread to fix the dark instrument cluster on my 2011 Elise. Pulling and replacing fuse 8 worked the first time. I thought about recent activity in the car and remembered this bit from section MP in the service manual (pg 17):
Disconnecting the Battery
If the battery is to be disconnected, the following precautions should be taken:
i) Wait for at least ten seconds after switching off the ignition to allow the engine management system to
adjust the setting of some components ready for re‑starting.
Just prior to the instrument cluster going dark, I had been at a rest stop eating lunch. I got my car's electrical system confused with another...I thought that if the radio was on and you turned the ignition off, the radio (normally operated by switched power) would stay powered until you opened a door. When it didn't work that way, I switched the ignition on and off about 3 times (starting the car maybe once of those 3 times), experimenting with different conditions to verify that functionality was not present. I'm pretty sure I switched the ignition on and off at less than 10 second intervals. The next time I stopped and then returned to the car, the instrument cluster was dark.
So my hypothesis is that if you switch the ignition on and off at less than 10 second intervals (and in my case, not always starting the engine), you may induce a condition that causes the instrument cluster to go dark.
If this is a programming bug, it would probably be something like a file needed for start up is corrupted, and another program depends on no errors in that file before it will enable the instrument cluster. Then once the instrument cluster fails to work, it stays dead until it gets reset by removing power (pulling fuse 8). If in fact a start up file (that is written to in that 10 second window) exists, corruption is apparently not a problem for the rest of the system...the car always started and ran normally throughout the sequence of events I experienced.
So if you experience a dark instrument cluster and stumble on this thread to fix it, reflect on what happened in the immediate past and chime in with whether or not you might have had a similar experience to mine.