Obviously, you need to disable the screen element by taking its fuse out. The screen takes a lot of current - at tickover you can hear the revs drop when you switch the screen on! If its left on it'll cost in fuel. But do you mean that it's not switching off automatically, but you can still push the switch to switch it off? if you can switch it off with the switch, then the relay is ok and the timer is faulty. My thoughts would be to accept that that's the case and just remember to switch it off once the screen has cleared. (like we used to have to do on older cars!).