Saw someone had a question about this and decided to post this for anyone else who needed the info..
THIS DIY assumes you know how to connect your AMP
1 Amp (for your subs) Including the following
[1 power wire, 1 ground wire, 1 remote cable wire, 1 RCA wire]
1 Lineout Converter (speaker level to RCA)
1 Wire Splicing tool
Wire Diagram of your stock radio harness
Purchase a lineout converter to RCA- pretty much its 4 wires two positives and 2 negatives that come out of a little box with two RCAs... just go to best buy or your local electronics store and tell them you want to hook up a sub to your stock radio and you need a lineout converter to RCA thingy.. theyll hook u up.. should be no more than 20-30 bucks... or find it online cheaper
Buy a Wire Splicing tool (make sure its for small cables 16 gauge and up)
Locate the rear speaker wires on the stock radio harness (behind the radio)... these are the ones you want to tap into
the rear speakers wires on the stock harness for the 2012 civic lx are
Yellow and brown for the driver rear, and Blue and orange for the passenger rear.. (You can confirm this on your specific car by just opening your trunk and taking a look at the wires that connect to your rear speaker...simple enough)....Splice those wires on the stock radio harness behind the radio.... and connect the wires on the lineout converter to it
remember keep negative with negative and positive with positive...if you dont have a meter to let you know.. just check in your trunk under your stock speaker which side is the negative and which side goes to positive..
Now jus plug in your RCAs coming from the AMP to the RCA inputs on the lineout converter
and thats it... your done.. and of course you have to have an amp powering your subwoofer
PS. To give remote turn on power to your amp just connect your remote cable to the remote turn on wire listed on your diagram ) On the 2012 civic LX its the purple wire on the stock radio harness