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How to add a subwoofer to a factory stereo

Get great sound while keeping your factory controls

Adding a subwoofer to your factory stereo is a great way to improve your sound without giving up your familiar factory controls. In this video, you can follow along as one of our experts installs an amplifier and subwoofer in a car with a factory stereo. You'll see all the basics of amplifier installation, including:

  • How and where to run all the wires
  • How we get the power wire through the vehicle's firewall
  • How to get the audio signal from the factory stereo to the amp with the help of a line output converter

If you have any questions or need help selecting the amp and subwoofer that's right for you, contact our advisors. They're available via phone and chat, and will be happy to help. 

Read video transcript

Hey, I'm J.R. We're here in our install bay, and we are going to install and amp and a sub in this Mazda. now the process is pretty much the same in most cars. We're going to go over the basic steps what it takes to install an amp in a sub in this particular car. We've got the factory stereo, so let me go over what we're going to do here.

First, we're going to use the power wire and the ground wire to run power from the battery. The battery is under the hood in this car, and we're going to run power wire from the battery, through the firewall, down the passenger side of the car, all the way into the back into the hatch area where we're going to install this.

We're going to run an equally sized wire to the ground...we're just ground that in the back of the car, probably to like a seat bolt or something, and then we'll run a little blue wire to turn the amp on and off with the radio. We'll also need to get music into this amplifier, and that comes in right here to these RCA inputs.

In this particular car we have a factory stereo, so we're going to need to convert the speaker wire coming out of the back of the factory stereo, which will plug in right here on our line output converter. This will change it over to our RCAs, which come out the other side. If we had an aftermarket stereo, that stereo would have RCA preamp outputs already on it that we could use to connect RCA cables directly from there, and run them to the back and plug them into the inputs on the amp. Since we don't, that's why we need the line output converter to convert speaker wire into our RCAs.

These are the RCA cables that we're going to run from the line output converter to the amplifier, and of course, we don't want to run our RCA's right next to the power wire. That's a great way to get noise introduced into your system, which you do not want.

To get music from the stereo into this line output converter, we're going to use this speaker wire here. And then to get music from the amplifier into our subwoofer, we're going to use this thicker heavier gauge speaker wire here because we get a lot more power. We need thicker wire. And then lastly we're going to run this little remote bass knob so that the driver can crank the bass or turn the bass down as the song dictates, and we should have a pretty sweet little sub system added to the factory stereo. It's going to sound pretty darn good.

All right, so the first thing we're going to do is disconnect the negative terminal from the battery, so that we don't shock anything or blow anything up. It's a ten millimeter socket here, it's probably enough. All right, tuck that away so it can't touch anything bad, and the next thing we're going to do is we're going to run this power wire. You can see it's got a nice power ring on it. This is the positive terminal of the battery. We're going to connect it right there between that nut and that stopper right there, so that's going to hold our power wire secure to the positive terminal of the battery.

We're going to run this power wire up through here. We're going to put it in some flex loom to keep it protected from the heat of the engine. We're going to install a fuse somewhere in this neighborhood right here that will keep our entire vehicle safe in case there's any kind of short in the power wire, all the way from the front of the car to the back of the car.

We're going to run it over there, to a nice big huge grommet in the firewall where a lot of the factory wires go from the engine compartment through the firewall and into the passenger compartment. We're going to use this knife to poke a small hole in the rubber next to the wires, making sure not to cut any of the wires of course, and then we're going to poke this coat hanger through so that we can fish our wire through the grommet.

So let's see here, all right, that should do. I'm going to take this coat hanger, and I've already put a little hook on it. The idea here is that once we get the coat hanger through and we find it on the other side behind the glove compartment, we're going to take this power ring, just hook it on and pull it right back through. That's the idea, hopefully it works out just that easily.

All right, got the coat hanger through the hole and I'm pushing it through pretty much almost all the way, so just there's still enough for me to grab on this side and pull it back once I've got it connected to the power ring on the other side. So now we're going to go around to behind the glove compartment see if we can find our coat hanger and that hook to hook the wire on to. All right, let's pull our wire through. Oh yeah, just like it's supposed to work.

All right, so we've pulled enough wire through to get over to the battery, and we also need to install a fuse holder. The amplifier wiring kit comes with a pretty nice fuse holder with the screws installed, so we're going to have to cut this wire somewhere. You want to do this pretty close to the battery. The closer the battery the better. We don't need it very long. See if these wire strippers will do the job, sometimes they didn't work on super thick wire like this, but they worked pretty nicely on that one today.

All right, so now we're going to need an allen wrench, tighten it on down. All right, power wire securely attached to the fuse holder. No extra strands of copper hanging out on either side, so a nice clean thing. Then we put the cap on it for now, but we can just attach it since we're going to screw that right down into there. And now we can go ahead and connect this to the battery.

All right, power wire is now securely attached to the battery, so let me put our fuse holder right there. Just a little bit of slack there, and now we can install the flex loom and get this wire attached up here, probably with some zip ties.

All right, so we've got the power wire through the firewall, we've taken care of it all under the hood there, now we just need to get it routed from behind the glove compartment, down the door sills, through the car, all the way to the back where we're going to actually install the amplifier. I'm just going to lay the cable out along the route here, we might have to pry these panels up and stuff, or we might be able to just kind of tuck it under there. I am using a little tool to sort of help it get tucked under there, but so far I haven't had to actually pry any panels out.

All right, so we've got our power wire run back here to where we're going to put the amp and the sub. As you can see, it's routed right back to here. We're going to connect that right to the power connection on the amp.

That's the power side. Now we've got to figure out where are we going to ground this amplifier. So we've got a short little wire, we want to ground this to a good bolt that goes right into the chassis of the vehicle back here in the back. Looks like the bolts and this surface are painted. We cannot have paint between the middle of our power ring and the the chassis ground, so we're going to want to sand that off. We're gonna use some sandpaper to sand the paint away so we've got bare metal. You really need a good ground anytime you're installing anything into a car to complete the circuit and make sure you're not getting noise.

So we've sanded the painted surface down to bare metal, we've sanded this bolt head down to bare metal, we should be able to go ahead and put our power ring on it and screw this back into the car and we will have our ground connection. All right, good and tight. We've got our ground wire got right next to our power wire, we can go ahead and put the trunk of this hatchback back together.

All right, so we've finished the power and ground, which is kind of on the other side of the car. And that's kind of the first half, or the big part of an amplifier installation is getting that power wire run from the front to the back and finding a good grounding point.

We've got all that done now, and we're going to work on getting the music from our factory stereo in this car into the amplifier, which means we're going to take the dash apart. For that i'll use the Crutchfield MasterSheets, which will show me how to get the dash apart and we'll get into the back of the radio where all the speaker wires are, and we will tap into those wires so we can connect our line output converter and grab a copy of the music and send it out into the back to the amplifier.

All right, so we've got the factory stereo out, we will set that to the side and we have revealed our wiring harness and we've identified our speaker wires. We're going to tap into those using these Posi Taps, which make connecting to factory wires like this much easier than actually like cutting and splicing into them.

All right, so there's our four taps for the factory speaker wire. We'll get some aftermarket speaker wire, and we'll get those attached to the other sides here. The next thing I'm going to do is to connect our power wire we're going to use, about a foot or so, plus this blue power wire that came in the amplifier wiring kit. And last, some ground.

All right, we've got rear speaker wire positive and negative, got connected to the ground wire, we've got connected to the power wire, we're going to run those wires just long enough to get to this line output converter. We've found the space in the dash that should fit perfectly. We've even checked it to see, so I'm going to go ahead and start connecting them to these terminals on this line output converter.

All right, now I've got all those connections made, we are ready to run the RCA cables up through the dash here, and you may notice we've got four RCA connectors on this line output converter. There are actually four RCA outputs, now it is just a two channel line output converter, so and all we need for what we're installing today is this set of outputs right here, the bass output, because we're installing a subwoofer amplifier. This conveniently has an extra set of RCA outputs which we're going to go ahead and run the cables for, in case the owner would like to install an amplifier later.

So we've got our line output converter wedged nice and tight in the dash here, and we've got our RCAs and our remote turn on wire. We started running them down through the dash right down here to by my feet, and now I'm going to get down and get underneath and start to run them on the side of the car all the way to the back.

All right so we're going to run the RCAs and the remote turn on wire down this side of the vehicle. We're also going to run the remote bass knob control wire right along with them. Some amps have it, some don't. Sometimes it's an option, so this may or may not be a step you'll have to perform when you install your sub and amp.

And so, just like we did on the other side of the vehicle, now we are tucking these wires up underneath these panels. All right, so we've run our RCA cables up the driver's side of the vehicle, along with our remote turn on wire, and we're going to go ahead and connect everything up at the amplifier now, because we've got all these wires all back where we need them.

So we'll start with the RCA wires, and these will just go right into the RCA connections on the side of the amplifier. On the other side is where our power and ground and speaker wires all connect, so we'll start with the power wire, that first wire that we ran. Go ahead and strip it up with an Allen wrench so that we can use that to tighten down these wires and our power wire. Let's do our ground wire next. All right, and last but not least our blue remote turn on wire. All right, so all those are connected good and clean and solid.

So all that's left now is to connect our speaker wire from the amp to the sub, and I've got some speaker wire right here, and we'll go ahead and strip the wire speaker wire. Securely connected to the amplifier. All right, we are hooked up. We are ready to reconnect the negative cable on our battery.

And just to recap, we've run power wire from the battery over on the passenger side of the vehicle all the way back to this amplifier back here. We grounded to a seat bolt right here back by the amplifier, and then we grabbed speaker wire signal from the factory radio in the dash, connected that to a line output converter right behind the radio, and ran RCA cables and our blue remote turn on wire from behind the radio, down the driver's side of the vehicle, right back here to our amplifier. We've got all of that connected with some big thick speaker wire going from the amplifier to the subwoofer to make bass, and now this car is actually going to sound decent with the factory radio in it.

So there's a great enhancement. So if you need any help picking out an amp and a sub, or any combination thereof, check out Crutchfield give us a call we can certainly help you get the right stuff. And of course, we can help you get it installed as well.

  • Kathryn Yort from Kamuela

    Posted on 6/10/2021

    Any idea what the speaker frequency range or receiver voltage output is for the stock system on 2014 Honda CR-V w/ 4 speaker?

  • Matt G

    Posted on 1/2/2021

    I have a 2002 Tahoe with factory amp/sub (non Bose). I would like to eliminate the stock sub and wire my mono amp/sub but keep the factory head unit and use factory amp for speakers. My question is which speaker wires do I tap to convert the line output converter to RCA cables? Would I use the factory subwoofer +/- before factory amp?

  • Rob from North adams

    Posted on 10/21/2020

    It would be a huge upgrade to this section if you could refer to which speaker wires on the factory harness are the more proper wires to connect to? My car has two fronts and two rears in the doors. That's it. I connect to my Rears? That would be my guess. I'm guessing if you had rear deck speakers them might be the ones? If there's any way to improve on specific speaker wiring connection that would be great. Or if I could get some help in the comments? Thank you guys! You guys are great I've placed five orders this week from you LOL

    Commenter image

    Alexander H. from Crutchfield

    on 10/22/2020

    Rob, your purchases entitle you to free tech support. Give us a call and someone can give you one-on-one help with your wiring.
  • corn from South River

    Posted on 9/21/2020

    But how will this setup affect the sound quality ? and the way the sub hits ? Would I get better sound quality with an aftermarket headunit ? Will connecting the sub by tapping into a speaker give the same quality and punch as connecting it into the right port on head unit ?

    Commenter image

    Alexander H. from Crutchfield

    on 9/30/2020

    Corn, as long as you can tap into a full-range signal, a line output converter can give you a solid array of tools to adjust the low frequencies to your liking. The right aftermarket head unit can give you those tools as well. If you can't replace your head unit, a line output converter is a great option.
  • Pieter Maritz from Hermanus

    Posted on 8/31/2020

    Hi, where do you connect the blue turn on wire at the back of the factory radio?

  • Soul Odoms from San Antonio

    Posted on 8/30/2020

    if i add two subs and an amp to my factory deck, will the bass drown out my hi's and mids...

    Commenter image

    Alexander H. from Crutchfield

    on 8/31/2020

    Soul, if you incorporate a bass control knob, you can adjust the bass on the fly as you listen to different music.
  • Will Tuten from Round O

    Posted on 6/24/2020

    So the blue wire running to the remote for the amp, is it coming out of the LC2i remote hole to the amp or is it just an accessory power wire coming from the back of the head unit?

  • spencer from austin, tx

    Posted on 5/23/2020

    When he taps into the speaker wire with the positaps, I can't tell if he is putting all 4 positaps on the same wire from the wiring harness or on different wires...He only showed one wire (the white one), but it looked like the positaps were installed on multiple wires. Can you explain in more detail what he did here?

    Commenter image

    Alexander H. from Crutchfield

    on 5/25/2020

    Spencer, he's using each positap to tap one wire each, one wire for each rear speaker signal polarity (rear right +, rear right -, rear left +, rear left -). That left/right signal feeds into the line output converter for use with the amplifier of your choice as he goes on to explain. You can find out more about line output converters in this article.
  • Ruben from Riverside Ca

    Posted on 4/20/2020

    I got a amp and sub installed in my 2014 Subaru crosstrek and for some reason when I turn my volume up past a certain point I get a cracking noise

    Commenter image

    Alexander H. from Crutchfield

    on 4/23/2020

    Ruben, if you bought your gear from Crutchfield, you can call Tech Support for free help troubleshooting your system. If you purchased your equipment elsewhere, you can still get expert Crutchfield Tech Support - 90 days-worth for only $30. Check out our tech support page for details.
  • Chris from Perth,W.A.

    Posted on 1/15/2020

    I cant help thinking that connecting your power cable to the battery then running it through the car to the boot runs the risk of shorting it out against the chassis .... Could cause a few people a problem ????? And any run ins with other positive constant 12v cables encountered along the journey of removing the dash. Id suggest disconnecting the battery entirely. Or connecting the power cable to the battery after tunning it to the boot and connecting it to the amp.

    Commenter image

    Alexander H. from Crutchfield

    on 1/16/2020

    Chris, that's a good option. Thank you for suggesting it.