Im assuming its on the left hand side of tge boot behind the carpet near the light wiring or same location but above the rear strut mount
As the tail gate wiper, and heated rear screen wireing harness comes in at roof level from the cabin, I would not have thought a wiper relay would be found left hand side of the boot. Like I said, I've had the side carpeting of when installing rear parking aid.
Arthur are you saying it could be in the pillar that the rear light cluster is set into? I cannot see it being there. Must say as it's quite a common complaint, I would have thought somebody would know where this elusive relay exists. If it does exist at all [which I very much doubt it does] Would have though one of the "I'm a trained Ford Techie" bods who vist the forum would have a definitive answer to the "is there a relay or not" in the boot area.