No idea without a play to be honest ,but a quick solution is to disconnect the feed from the relay and run a new feed direct from the ignition switch to the relay so you turn off and the fan goes off ,without a good play to find the problem i cannot tell you and you may need one of these new breed of mechanics who never get dirty but walk around with a laptop under their arms and talk all geeky junk .Unlike us oldies who only think and talk about cars and women and whos done the coldest call out up the motorway in winter and done the biggest bodge to get a 40 ton truck home safely