Cut the ground wire (black) going to the corner.
Then find the cut end of the black wire coming FROM the corner, NOT the one that goes back into the harness to ground.
Then tap that end of the black wire FROM the corner to the hot wire of the turn signal as described in my post above.
(If the black wire is making the fuse melt, then you are wiring to the wrong cut end of the black wire.)
If you do this right it will work