I first tried the Pin 6/16 instruction from the note below to install the ASWC-1 Steering Wheel controller but it didn't work for me.
Instead, I followed the "Altima sedan 2013-up / Rogue 2014-up only" instructions from the AX-NIS32SWC-6V (Backup Camera). Basically, you throw away the harness that comes with the ASWC-1 and use the harness that comes with the AX-NIS32SWC-6V to connect to the ASWC-1 control module instead (it is pre-wired for this).- Steering Wheel Control Adapter: Axxess ASWC-1
Please use this link from AXXESS to connect the steering wheel controls adapter. It didn’t work for me initially but I swapped the Gray/Blue wire to Pin 6 and Gray/Red to Pin 16 and it works perfectly: https://metradealer.com/files/aswc/ASWC-1_INST_860.pdf
This doesn't change any of the parts you need to buy from the above list - except that you can get away with the more basic version of the 70-7552 speaker/radio harness that is more widely available from Metra because the Steering Wheel control is wired through the Backup Camera harness on the Leaf instead of the speaker/radio harness.
By the way, my new head unit is an Alpine ilx-007, in case that's of interest for people...
Hope this makes sense and is helpful ... cheers!