Steering Wheel Controls - JBL - Atoto A6

I've found bits and pieces of info. Apparently this works without the adapter (which is now $59 that I'd rather not buy).

My Atoto A6 has two steering wheel control wires. I understand that the 20 pin harness (the one you put the resistor in) from the car has two steering wheel wires (the pink and the second white), which I've tried connecting to and couldn't get to work.

Does anybody know if I also need to connect the ground, which is the red wire in the harness, to a ground source?