From early 2001 the diff lock mechanism was dropped until 2004.
With a pre 2001 Disco 2 , the difflock warning light is installed operational . That is if the diff is locked , even with a 10 mm spanner , the light will indicate.
With these models , if the car is started before the diff is locked , TC will stay operational. Otherwise it will trip and the 3 amigos light up. They reset if the car is restarted with the diff unlocked.
It is a useful function being able to trip the TC if required. General consensus in South Africa is that TC is a serious no-no in sand - but I guess not much of that in the UK ?
Dave