the rear numberplate light runs directly off the headlight switch
grey / green wire
seperate fuse = fuse 18
your rear tail lights also run directly off the headlight switch [obviously] but have seperate fuses but there is a brown wire used for both the number plate as well to earth - the estate version has a separate earth point though m8
and for your instrument panel illumination it has a feed from fuse 22
there is a brown wire that runs to the multi timer from the insturment panel that creates the circuit / switch for your illumination - i would start here and work backwards - could be a simple diode that has popped /damaged on the back of the instrument panel