I now have the steering wheel controls and reverse camera trigger (but not the camera itself yet) all hooked up. Amazon was taking ages to ship my AWSC-1 universal steering wheel kit but @Siridar suggested I may not need one so I cancelled the order.
I ended up finding the service manual and confirming the factory steering wheel controls are just a resistor ladder and should be compatible. I grabbed a 3.5mm audio cable from Officeworks for $3 and cut the ends off to use the connector. Strip the insulation back with a wire stripper and solder/crimp the grounds together. Solder/crimp the steering wheel A signal to one of the two remaining wires, and the B signal to the other. My adapter already had these wires loose for easy connection but if yours doesn’t you may need to cut into the factory wiring.
Your head unit should have some way of “training” it to recognise the buttons. If your head unit doesn’t have this feature you’ll need a universal steering wheel control adapter. After making the Sony unit learn the buttons it worked well!
I also hooked up the reverse trigger from the Leaf to the input on the Sony unit. I couldn’t find the 6v power supply so didn’t connect up the video signal yet. I’ll have to find it and hook it up another day.
Useful pages from the service manual:
