The studs go through the plastic and touch the case enough to provide a ground path. I get 0 ohms with my meter when I touch the stud and the case. Maybe not the best source for a ground, but how many working radios are missing the "L" bracket? Thats the back of the stud in the lower right. Photo is the back of the chrome bezel. ?
My car was missing the "L" bracket, I had to source one from another car. I'm guessing most cars usually have those missing that had aftermarket radios installed.
