For what its worth, Nick at Austin's, in his account of how to fit a camera, says this " ...The harness runs through the RH tailgate washer tube gaiter ; the LH one already has too much harness bulk used here...."
The unit he was fitting, several years ago now, was a BMW BM54 (Becker) / Mk4 DVD / 16:9 Boardmonitor, but you may still find something useful if you read his "Featured Car" page here: http://www.austingarages.co.uk/featured_car.html
David