Gareth,the interior light switch usually has 3 positions: 1- on all the time,2- off all the time, and 3 -on when a door is open. I'd say there's a short in the back wiring, probably near a door -activated switch button, so current can flow to earth as if the door is open. The front seems ok,if I understand you correctly. You need to put the main switch in the "off when doors are shut position" and fiddle around the door button at one open door at a time, with the other doors shut .
Martin
October 2009
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