License plate lighting - cable breakage ?

Hello.
I'm just busy making my newly acquired V8 float again. It's gonna work out all right.
Only with the license plate lighting I break my fingers and my head

The light on the driver's side only burns when I pat the tailgate from the back friendly on the shoulder and then stays on no matter what I am on the road then instead. When I turn off the light and turn it on again, my fat guy insists on this friendly greeting before he starts the journey with me in the dark.

Since I don't want to get too involved with him, I've been looking for the source of the error. All contacts cleaned and ventilated on a fixed seat, even the pear. I wobbled on the cable from the outside and under the sheet metal to find a cable break. Don't know! If the pear burns after the friendly shoulder knock, then there is nothing to find.
Also in the search here I found no post with the same problem.
Has anyone already described this problem and not here? I'd be glad to get every tip so I don't have to rip out the harness for nothing. Although I don't know why, because I've already measured it on mass and tension. But only in the back.