try these links
http://www.landrovernet.com/forum/showthread.php?t=4303
these are the repair bar i was on about
http://www.roverconnection.com/Disco%20Acc%20Pix/rcdsh.htm
has your car got dim dip lights when engine running and side lights on .
if so try disconnecting dim dip relay unit , unsure were it is on discovery , but on rangerover it is above drivers feet .