Interior Light problem

Can anyone advise on a problem i have with the interior light on my 2000 freelander.
The light comes on as normal when the door is opened - but the map lights and main light will not work other then that - I have replaced the unit with a working (checked) second hand part but still no joy - I have checked the fuse and that is fine - am i missing something else simple.
Any help or pointers would be great.
Thanks

sounds like a bad earth.circuit has 2 earths,door switch is one,other must be duff.