Two possibilities , short to ground on the black with yellow trace wire or the rear electronic module is shorted to inside to ground . The easiest way to find the problem , find the rear electronic module an disconnect connector C420 e ,if the light goes off the problem is with the module , if not wire is shorted to ground. Does this sound complicated ? It's not really . The (REM) this module is located in the trunk. Remove the carpet lining on the passenger side of the trunk, the module is bolted inside the quarter panel. You will need to look at a wiring diagram to double check the wiring (so you know which connector to remove) Here is a web site for free wiring diagrams http://www.bbbind.com/free_tsb.html
Enter vehicle info. year , make , model and engine size. Under system click on lighting , under subsystem click on turn signal lamps .Then click the search button ,then the blue link . Scroll down to the fourth diagram . At the bottom of the diagram you will see the rear electronic module .On the top ,right side is the grounding wire for the right rear turning signal ,connector C-420 ,C stands for connector . The wire is in pin #4 of that connector . Find that connector an disconnect . Does the light stay on or go off . Let us know what happens .