Magtor

I read most all the post I could find about this radio wiring diagram. I am missing the clip piece at the end of the wiring harness in my 92 mustang. So im left with a total of 7 wires for the speakers, but I'm not sure which are grounds. I've tried a bunch of things and I know its not the speakers.
Used http://www.veryuseful.com/mustang/te...Radio_diag.gif and http://www.installdr.com/Harnesses/Ford-Wiring.pdf as my resources but i still can't figure it out. Any help?