As it is fused, check this first as the actual output of the relay is after the switch.
If fuse is ok then check for live and earth at the window itself.
I don't know if your year of escort uses the "pin" and "pad" system to transfer power to the screen/wiper etc, but if not a fave thing to happen is that the wire breaks just inside the grommet that goes between the tailgate and body.
I have done a few mk4 escorts that did this, but most broke inside the insulation so you could not actually see it, but probing along the wire soon found it.
tabetha