When you first got him did you get any information about his previous owner ? Home situation, why he was given up, that sort of thing ?.
I don't want to sound like I'm blaming them, but it could be that he did have his own `spot` on their sofa, that no one else ever sat in. It's been a few months, he feels more settled and secure and that he can now claim `his` spot.
Teaching him to share his space, as well as allowing him to share yours ( only when invited) might be the way to go.
As for the wires thing, I hate to ask, but were there any physical signs of abuse ? Wires, cables, brooms, belts, even coat hangers have all been used to hurt dogs all over the world. You wouldn't be the first owner to suffer for someone else being abusive. We got our girl when she was only 10 or 11 weeks, there were no physical injuries, but she's still terrified of laud bangs and sometimes flinches if you reach out to pet her. I don't know what happened to her before us all we could do is work on getting her to trust us, we're getting there..... slowly.