Looking for help to connect the am/fm ( stock) radio in my car. The previous owner clipped the harness, I never tried to replace it because with the top down and the big exhaust rumble we could barely hear ourselves talk. Now I am wanting to get it working.

I have a copy of the service manual pg. 15-28 showing the wiring layout. However without the wires to the instrument panel , and no harness, how do I wire the gray into a rheostat. I can hook up the yellow to a power source. Hope I am asking this correctly cause I hate electrical issues . thanks Larry