You will need the harness and the kit (brain) for your year of production. When I attempted this on my car (2012 Si), I ordered the following:
08E91-E22-101A Remote Start Kit (known as the brain)
08E92-TR0-100 Remote Start Attachment (the harness that will attach the brain to the car)
(Optional) 08E91-E22-1M001 Remote Start Transmitter (the kit comes with one, but I wanted a second one for the second key).
Unfortunately for me, it did not work despite everything connecting without issue. And, every schematic I have looked at says it would work if I bypassed the clutch safety switch; yet it does not. Furthermore, while everything I had said the remote start system was compatible with the Si model; this was actually incorrect and was an error in the catalogue (unfortunately, I found this out after I had installed everything, so now I'm stuck with it and cannot use it). My saga is in this thread:
First, my apologies if this is a repeat; I did search the forum a bit on this topic but did not find what I was looking for to answer my questions. I have a 2012 Civic Si which I would like to add a remote starter to; my preference would be to buy the factory optioned system and retrofit it...
9thcivic.com