This is the grounding location that I used (where the arrow is pointing). I'm not sure why my finger is pointing to the screw on the other side ??? The thin wire and electrical tape was just temporary. There is now a thicker wire with a proper waterproof crimp connector. I have a thicker wire that I'm running to a fuse junction box that I have behind the stereo. The fuse junction box then runs +/- wires to my Defi gauge control unit, my autodim mirror that I swapped in, and soon to be laser jammer. I don't have any ground loop interference. I don't know if the Brainiac kit deletes this bracket. If so, you should be able to see where the bracket itself touched metal, and then use that point.
I was taking a look while someone else was installing the Brainiac kit and they were having a ground loop problem as well. I don't remember what they did though