Connecting a JoyCon to the radio harness on my car and reading through all the available material that I could find, I kept running into some problems with 12v going into the JoyCon instead of measuring the resistance. Here is how I connected my JoyCon EX to my steering wheel controls on the factory radio harness.

GM24 Radio ConnectorRemember, this connector is viewed from the pin side, not the wire side.

Connect the DATA (white) wire from the JoyCon into pin A6 and then the GND (black) wire from the JoyCon into pin A7.

JoyCon ConnectedMight be a little hard to see, but the yellow wire in my harness is connected to the white data wire, and my orange wire from the harness is connected to the ground of the JoyCon.