To make a long story short, I'm returning the botched wiring in my '85 S to stock. The only remaining piece of the puzzle (thank goodness for the factory wiring diagram) are the grounds located in the center stack. I have three black wires with ground lugs (one is bolted to the frame of the dash from behind, the other two are just hanging out) which are cut off. Where should these terminate? I assume the two floaters with lugs are for connecting the radio chassis to the dash frame via the terminated one, but I'd like some sort of confirmation.

 

Just to update this, I connected these ground wires (from the dash frame) to the back of the radio and tape deck using an M5 threaded hole in the back of each unit that I assume is meant for this. I did some other work too, but my radio reception improved so maybe this was part of it.