Maybe the sel sub wiring is present by the spare tire
Reply :I can't speak for any other trims or radios but the base S is pretty easy to install a subwoofer in. Here is what I bought and what I did:
Subwoofer installation kit, you really just need a fuse, fuse holder, decent thick wire, some terminal lugs, a short piece of RCA cable. It was cheaper for me to buy the kit for the fuse holder, fuse, and RCA cables than those three ala carte. I was using my own wire. You will not need a remote wire if you buy what I list here. I ended up running one and not needing it. I had to find some wire to go from the left rear speaker wire to the back, 2 wire 18 gauge or whatever. $15
Subwoofer and box. I have a Kicker 10c104 from a previous sub install, it was in a way too small box but I did like how it was much smaller. The "correct" box size (1.25 sqft) is very big in the trunk. I think the other was smaller than 1 sqft. The box was made out of some MDF I found in a dumpster. $70 but this will of course vary with what you buy, I had this stuff on hand.
Subwoofer amp. I bought the cheapest monoblock amp with decent reviews, a Blaupunkt AMP1500M. I think it's like 450 "real" watts and is also 2 ohm stable. It was $62. It also has a built in low pass cross over.
Speaker level converter. Everyone seems to like the LC2i but the Blaupunkt EP1700X is almost the same for $37.
Zip ties, basic hand tools, 10 mm wrench, etc.
Ok run the bundle of wires from the front to the rear, I ended up pushing out the grommet in the firewall for the clutch peddle (you will lose it, grab it with pliers and pull it out), then I pushed the power wire up into the engine compartment. I zip tied the fuse holder on top of the ECU next to the battery. Don't connect it to the terminal yet.
Gather up everything (don't forget your remote wire) and pull up the trim in the front and the back door sills and pull out the rear seat bench, pull the trim away from the rear upper seat area. Fold down the left rear seat. Push the bundle down along the wire harness, behind the seatbelt anchor, then up along the wheel well, and use a stiff wire or coat hanger (be careful) and push it through to the access hole in the left side. Pull through all your wires. I found the wires that feed the left rear speaker, they are a twisted pair of grey and brown with a grey stripe. I stripped back 1/4" of insulation, tied my wires down and soldered them and wrapped them in tape.
I ended up screwing the amp and converter to the box and wired it up inside and then I brought it outside and hooked it up. Eventually I will have a power disconnect plug so I can take it out easily if I need the whole back.
So the EP1700X (and the LC2i) have an auto-on feature when they detect audio in the left channel input. That will turn on the amp if you wire the remote-out to the amp's remote in. Easy peasy. Put your positive lead on the amp and run a positive wire over to the EP1700x, do the same with a negative wire you screw down to something grounded (I used the metal tab inside that same access door on the left) and run a negative to the converter. Put your speaker inputs into the left channel on the converter, screw down your positive cable, watch for smoke and fire (kidding!), and turn on the radio. Then if you are using your remote control box, I put mine right next to the hood release in that little corner.
That should be pretty much it and you didn't even have to remove the radio!
The most important take-away is the wire colors which are grey and brown with grey stripe, twisted together. I didn't bother with the other side so you're on your own there.
I should add that this, as the kids say today, "slaps." This 10" sub has way more bass than I need.