On the R/BLK wire.
I also was pretty sure when I saw it lose (but with duc tape), that would be the solution. BUT then I was thinking, why would someone remove it and duc tape it, unless it was deliberately. And if it was done deliberately, what would happen if I connected it. So I decided to read some more posts and found this one.
See attached image, it's a technical bulletin.
And it seems to indicate the R/BLK wire shouldn't be attached and be duc taped, just like mine is. Then I got more confused. And didn't dare to attach the R/BLK wire to the head light relay after all.