I have a 2013 Titan SV that I installed a Pioneer HU in shortly after purchase. At that time the wiring adapter in question did not exist. I actually installed an aftermarket BU camera which works fine. Another member of this site mentioned he was going to use that wiring adapter. I purchased one (it's presently on my desk) and am planning on installing it later this summer (the other member has since stated that it works well on his titan). I also installed the SWC adapter - the only function that works is Vol up and down, but it works.
The BU camera function will work without the SWC module present. connect the battery (accessory),and ground lead to the radio harness. Connect the BU sense wire to the HU BU sense line and the video connector to the BU camera input. The HU needs to be set to turn on the BU function when voltage is present.
I don't know this for fact (haven't taken time to check) but I think the Nissan BlueTooth module is interfering with the SWC module causing only the Vol functions to work. I need to disconnect the BT module (under the passenger seat) to see if this is true.