Did you already buy the part from Nissan?
If not, don't. Call (800) information and ask for "Air Bag Service." They are a national company that will install a generic air-bag cut-off switch for $400 total, including parts, labor and tax, and they come to your house to do the work. I am very satisfied with mine.
First, you need to get your government approval letter from NTHSA. Go to their website, download the form, fill it out and fax it back. It only took 10 days to get their approval. You need the letter when your Air Bag Service installer arrives.
P.S. I don't work for them. Nissan gave me such a run-around when I wanted the switch installed that I looked elsewhere.