You MUST have the Road Tech 660 to use the NIM; you refer to the Zumo 660 which won't work with the NIM. If you have the Road Tech 660, you can adapt the NIM to work on your bike by supplying the wiring HD omitted from the SESG2.
Take a look at the wiring diagrams in this thread; especially post #9 which shows the NIM circuit:
http://www.cvoharley.com/smf/index.php?topic=53364.0The wiring omitted by HD is the 6A/B connector; there is none on the SESG2, so you'll need to provide the wiring to the NIM that would otherwise come from that connector; or, alternatively, create the 6B connector (the parts necessary are available from HD) as others here have done (such as member TIF2).
When HD published the paper Parts & Accessory catalog (p. 623) for the 2012 model year, they did not have exclusions for the SESG2 for the NIM, CB, or XM accessories. It was only later when customers wanted to install those accessories and dealers were unable to install them per the included instructions that HD changed the website version of the P&A catalog that the SESG2 was excluded from the fitment information.
There are threads showing the wiring modification necessary to add the XM module to the SESG2. You would do the same except for the wiring needed for the NIM.
Carl