Hello again, you should have been able to post on the same thread as you're original question although from my side it appears you haven't viewed my original reply so I'm not sure what's happened there.
As the heater control lights and the time clock light up the headlight switch is sending power to the instrument illumination circuits.
Two fuses power these circuits, fuse 21 (15A) in the fuse box under the bonnet and fuse 88 (15A) in the fuse box in the car. Pin 9 of the headlight switch (blue/red wire) is the power out to the illumination, this goes to pin 4 of the instrument cluster connector.
Check at the cluster connector for 12 volts with the lights on, if there is 12 volts there check pin 17 (black/orange wire) of the same connector for a good earth, you can remove the cluster connector without removing the cluster but you do need to remove the lower dash panel.
If there is 12 volts and an earth then remove the cluster and check the bulbs, it's unlikely but possible the bulbs have blown, you can remove each bulb holder and check for 12 volts to it.
I suspect the fault is likely to be in the cluster connection or bulbs as the other illumination works.
Let me know through this thread if you need further advice and I'll reply as soon as I'm able to.