No heater controls illumination e.g the light tube to the centre knob or to the bulbs on the knob surrounds wired in series. From the wiring diagram the grey/blue wire appears to connect to the ECU and the heated seat switches and relays, hazard light switch so maybe the diagram is out of date. Advised that problem is likely to be the dimmer potentiometer on the instrument cluster however this appears to be working OK. Fuse OK and all bulbs changed. Grateful for any assistance.