sorry mate only just seen the thread n yea that sounds abit unusuall so try wot cabriolet say's have u a multi meter cos put it on ohm's n test the straight through the wire from end to end it should have a reading close to the same as when u touch both prong's together then from the sterio side to the bodywork this should have no reading at all, this way is easier but your best is to visually check it, n wot color is the extra wire n i'll look though the bible n let u no wot it must be cheer's