I haven't had my Disco all that long over a month and a bit now and on occasion I drive at night. All my dash lights work however I noticed none of the lights were on on heating/ventilation area except the air recirculation and A/C switch which always light up.
The temperature dipped below freezing last week and "BINGO" the lights were on, my three turn ***** and air blower switch for the first time. The temperature went above freezing the next day and no lights, till tonight when again they all illuminated with the freezing temperature.
I don't understand it, all my lights on my dash work and throughout the vehicle however those ones are a little odd. My clock doesn't work at all have one on order, so what the heck could it be??

Brit and Clover the Rover

 

Connector somewhere is temp sensitive. It may only be slightly separated, and temperature can make things move around.

 

it is a ghost

 

My 96 D1 would do that... some short or open of some sort. You could also tap the controls lightly, and they would light up or go out.

 

It's just telling you that it's now cold enough to need heat. Like one of those fancy climate control systems or rain sensitive wipers... ;-)

 

Enough fun - see page from RAVE, remove the heater controls plastic panel and the three *****, pull out bulb (#5 in drawing) and replace. It lights the ***** and the slide switch via a plastic track. While you are in there, if you take apart the front plastic shield for the slide switch, you can spray contact cleaner straight back. The switch contacts are vertical, and parallel to the fire wall. Fixes AC fan switch "wiggle to work" issues.