i sorted it today
the problem was the brown and black wire at the fan switch was suffering from green corrosion . i followed this back all the way across the front of the slam panel . the wire was finally good near the air box . i replaced this stretch of wire and job done . what was happening was this wire wasnt being switched to earth by the fan switch , so the fan relay wasnt getting the earth supply it needed to energize .
i also fitted a bypass switch just incase it gets hot on track days .
thanks for looking at my problem and the advise offered . i hope my insight might help another cozi owner in their hour of need .