This and previous posts might give the impression that some of the electrics in my new car are shot, as I seem to be keep posting about them. Apart from the faulty light switch, it is just that some of the consumables (bulbs) needed replacing. The latest I needed to address were some of the dashboard instrument lights. As expected in the Defender, it is easy to unscrew the instrument panel. As it turns out, the temperature gauge was dark because the bulb holder had simply popped out of the back of it. Otherwise the speedometer bulbs were replaced, rather trickily with the aid of tweezers. Still, as can be seen above, they are all working now. Assuming that my imminent service check reveals no nasty mechanical problems I will move onto upgrading other parts of the cab.
References
1. http://www.retroanaconda.com/landrover/2009/10/installing-defender-td5-gauges-into-a-200tdi300tdi/
2. http://www.retroanaconda.com/landrover/2009/10/td5-gauges-bulb-information/