had a transit with horn,lights,wipers,washers out,same year as yours,the main loom in engine compartment at n/s bulkhead was rubbed through and full of water and corrosion,had a word with friend at local main dealer and he said this was a common place for faults and also where looms travel at bottom of headlights was another problem area,not saying this is your diagnosis but worth a look anyway,good luck
wickham, August 2010