How to: Subwoofer installation

Running power:

Starting with disassembly. You’ll need to remove the passenger side running board. Pry here and here.



Then remove the kick panel cover. Pull up on the center of this pin with your hook tool, and then remove it. Then pull straight to the left to remove, it will require some force.
Protip: if either of the 2 green push pins stays with the car rather than the panel, you can (VERY GINGERLY) grip it with your flush cutters and pull it out, then put it back on the panel.


Then the back seat. Remove that visible 10mm, then pull up on the front of the seat while pushing down on the back. It’s kind of awkward. You’ll need to unplug a small wiring harness from the back of the seat once you’ve got it loose.

Pop the hood, remove the battery. This is fairly self explanatory, 2 10mms on the battery tiedown and a 10mm on the positive and negative terminals. I didn’t take a picture of this because I felt silly taking a picture of a car battery.

Now we’re going to drill our pilot hole for the power wire. Hopefully the picture adequately conveys where this is located, it’s behind the battery to the right of the big wiring harness. There’s not enough space to see where it comes out on the other side, so I stuck a pick tool through the hole and then reached my hand up on the inside of the car to confirm where it comes out. It pops out right about at the edge of the firewall insulation on the inside.

(note: there are a few factory grommets that could be used instead, such as the large firewall harness to the left. my main advice if choosing to go that route would be caution. nicking a main harness like that on accident is a very expensive repair, i’ve seen it happen.)


Now that we’ve confirmed our hole location isn’t going to go through something expensive, we can swap to the uni-bit. Have your snap bushing from your power wire kit handy, you will want to test fit it frequently while widening the hole with your drill. Once the hole is big enough pop the snap bushing into place.


Feed your power wire into the hole, then go into the car and reach behind the insulation to pull it through. You can reinstall the battery at this point, but leave the power wire disconnected for now. We don’t want to run a live wire through the car.

Now that the power wire’s inside the car we can start running it to the trunk. There is a convenient factory wire channel for us to use, use your pry tool to release these clips (there are 3 in total) and pull up the wire channel cover.

This panel is slightly in the way, but I didn’t want to fully remove it because it’s big and annoying. This is a new car and the clips are still nice and fresh so it will require some force, but you can just pull the bottom of this panel out with your hands. Run the wire around it, and under the seat. From here you should have your power wire in the trunk.

Tapping input signal (GR86 premium/BRZ limited):

If you’re using the speed wire I recommended, slice it open and pull out the appropriate length of 2 wire pairs. White and gray are the standard colors for FL/FR so i’ll be using those sets.

We’ll be accessing everything at the factory amplifier. There is a foam piece that is in the way held in by 3 visible push pins. Pop those up with your pry tool and flip the foam piece out of the way so you can access the wiring harness. Unplug the harnesses, and using your razor blade cut back the factory wire dressing a few inches.

There are 2 options for getting signal back here: high level or low level. If you’re not sure, use low level. High level will generally require you to solder your speaker wires to the high level input harness, and most people reading this probably don’t own a soldering iron. If you’re using low level, you can simply cut one end off your RCA cables, strip back the insulation, and splice the wires directly into the low level inputs at the factory amplifier. It will generally be fairly obvious what color wire inside the RCA is positive/negative. Alternatively, you can buy 2 female RCA pigtails on amazon for fairly cheap and just splice those in.
Amp turn-on is also found here, it is the dark green wire in the middle of the harness. You can splice the 18ga blue wire in your power kit into there.

Here are pins and wire colors:

Low level:
FL (+/-): ltgrn pin A3/yellow pin A9
FR (+/-): white pin A4/ltblu pin A10

High level:
FL (+/-): ltgrn pin A1/blue pin A5
FR (+/-): brown pin A2/purple pin A6

Pins are counted right to left.
The positives are all on the top row directly above their corresponding negative wire so verifying pins is easy.


When making your connections, use a military splice. This is the technique every (good) professional installer uses. I highly advise against using T-taps or any other hackjob wiring connector.

Start by stripping back a small section of insulation.

Use your hook tool to poke a hole through the center of the strands.

Strip the end off the wire you’re splicing in, and twist the strands so they stay together nicely.

Wire go in hole.

Wrap the wire around, then pinch the connection point to close the hole you poked.

Apply electrical tape. Less is more here, you don’t need more than about a centimeter of tape.

Once you’ve made all your connections, reapply factory wire dressing. Subaru just uses electrical tape, so this is easy.

Tapping input signal (GR86 base/BRZ premium):
See premium/limited comment for wire splice technique.
I don’t have one of these, so writing a guide for it is kind of hard. You don’t have a factory amplifier, so obviously you can’t get your signal there. You’ll need a 2 channel line output converter (you can buy one of these for like $15 at any best buy), since you don’t have a preamp level speaker signal to tap.
From what I can find, it seems like the easiest place to access the speaker wires would be in the door harness found in each kick panel. +/- are purple/gray on both sides, the top and bottom pins on the far right side of the harness. On the driver side, just disassemble the running board the same way you did on the passenger side for power.

Here’s some pictures of the passenger side door boot harness, driver side should be almost identical. That purple/gray set is the one we’re after.


You’ll also need to source a switched power source for amp turn-on. I didn’t take pictures of this, because I didn’t have to do it lol. The cigarette lighter behind the glovebox would probably be easiest. Remove the glovebox by unclipping the piston on the right side, then push the 2 sides of the glovebox inward to remove it. From there you should be able to reach your hand behind the cigarette lighter and grab the harness. The blue wire is your switched power.

Connecting everything:

At this point you should have everything you need ran to the trunk. We’re going to start with connecting power/ground. Using your razor blade, slice about half an inch down the end of each wire, and then around the circumference to remove the insulation.

Cut a section of heat shrink and slide it over your power wire, then slide an 8 gauge ferrule over the end. Ferrules crimp to the wire when we connect it to the amplifier to ensure the power wire doesn’t come disconnected, and also prevent any loose strands from sparking against things. Make sure the strands go all the way to the end of the ferrule, remove more insulation if necessary. You may also need to separate some of the strands and cut them off if the power wire is slightly too big for the ferrule.
Once the ferrule is on, slide the heat shrink over it and use your heat gun to shrink. The adhesive lining will help hold the ferrule in place until we plug it into the amplifier.

If you have an amplifier that has fork terminals rather than circular ones, you’ll need to crimp on fork connectors instead. A crimping tool big enough for 8 gauge may put you over the $120 price point overall, so keep that in mind. You may be able to jankily crimp it with a normal set of kleins.


Attach appropriate size ferrules to your sub outputs and amp turn-on as well. Insert them into their respective terminals and tighten the set screw on top of them well. This will crimp the ferrules to each wire. Once you’ve got your amp where you want it, liberally apply zip ties to harnesses and flush cut.
My amp is currently mounted with velcro strips, which seems to hold it well enough but ideally I’d like to build an amp rack for it. I’ve also attached some foam to the underside to prevent potential rattles.


Now we can connect our power wire up front. If you’re using the wiring kit I recommended, you’ll need to cut the power wire at the marked location and install your fuse first. Remove a 10mm from either 120a fuse on the battery terminal and put your ring terminal on there. Cut a little section out of the power terminal cover to make room for your wire.


And that’s basically it, just have to set your amp settings. A few general guidelines:

Bass boost should always be set to zero.
If you’re using a LOC or you spliced directly into the preamp inputs of your factory amplifier, set input level to low. If you’re running speaker wires directly into a high-level input harness on your sub amp, set it to high.
Turn DC offset off.
High pass filter is up to you, but I like to set it around 120hz.
Gain is the only thing I can’t tell you how to set, because it depends. It’s not a volume knob, you are matching input and output voltage levels. if you turn it up too high you will asplode your sub - when in doubt, turn it down. The nice thing about the kicker key amplifier I recommended is it actually has a built in feature that will tell you exactly where the gain should be set.