I'm speculating here, but are you sure the wire from 15 to the tab should be there? You may have grounded the case, which provides a path to ground for the temp gauge. What did the fuel gauge do?

If the trace goes from 15 to the tab, then I guess it's correct; but I don't recall that being a "ground screw" but more of a "continuity screw." Maybe it's the same thing?

I also know that the traces in the corner near the case screw and where your white wire is can "wear" due to friction with the case. Is it possible the white wire is being pinched and is distorting or cracking the traces there?