If you look on the back of the clocks, you'll see several rubber bungs with green and brown wires going through them. These are spread round the cluster and do the back lighting.

The other bulbs do the idiot lights, and are obvuiously grouped together and use various coloured wires depending on their operation.
_________________
MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball