Thanks for your pm - sorry that this valid question has not received more attention to date..
My thoughts - I have not got a wiring diagram and I think the lag II uses something fancy called multiplex wiring any how..
I presume you have tried the obvious such as checking the festoon bulbs are not all shot.
Seems starnge that the map reading lights work but the central one doesn't.
The light units simply click out from the headlining so access to the plug in connectors and contacts with the light box is easy.
If I get a chance mate I'll take some pictures of how to get the light units out of the headlining tommorow as I want to show off my led festoon bulbs I got recently after reading a post on here..
Anyone else got any tips ?