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How to connect an amplifier to a factory stereo

Tips for using your car's factory wiring

Factory stereo speaker wires

Adding an amplifier to a factory stereo often requires running a lot of new speaker wire — from the stereo to the amplifier and then from the amp to the speakers. This can feel like an impossible nightmare. Fortunately, we have a way to make it a little easier. 

This article explains how to connect an amplifier to a factory stereo. If you have an aftermarket stereo, you'll use a set of RCA cables instead of one of the 9-wire cables below. Refer to our article about adding an amp to an aftermarket stereo for more details. 

EFX 9-wire speaker cable

Multi-conductor cable to the rescue

Usually, you'll be installing a 4-channel amplifier with speaker-level inputs. The best way to connect it to a factory system is to tap into the stereo's speaker outputs for the amp's input signal. Then send the amp's outputs back to the stereo's harness, and on to the speakers through the factory wiring.

"All-in-one" 9-wire speaker cable from EFX makes this easier by including the wiring for four speakers and an amp turn-on lead all in one cable. Run two of these cables from the dash to your new amplifier. You'll need one for the amp's input and the other for its output. These cables will act like a "T-harness" to connect your amp to the factory system.

Remove the radio to get to the factory wiring

Behind the factory radio, you can access all of the speaker wires in one place. The radio's wiring harness delivers power to the radio and sends its output to the speakers. You'll need to identify which wire goes to which speaker. Positive leads are usually solid-colored wires, while their accompanying negative leads tend to be the same color with a stripe of a second color.

Please be aware that these wiring colors vary widely from one car to the next. If you purchase your new gear from Crutchfield, our Tech Support team can look up the wire colors for you. Give us a call before you tear apart your dash, so you'll know what to expect.

Connect the wires

Once you've identified each of the eight speaker wires, cut each one. Connect the end coming from the radio plug to a new wire going to the amp's input. Connect the end going to the speakers to the appropriate wire coming from the amp's output.

That means you'll use two of the 9-wire cables, one for the amp's input, the other for its output.  

Amp wiring with 9-wire cable

Amplifier in/out via 9-conductor cables go to the right, radio plugs in at top, and vehicle wiring goes left. (Even with my challenged eyesight and shaky hands it only took me about 40 minutes to wire this harness for illustration.)

Forget the turn-on lead

Amplifiers that have speaker-level inputs also feature "signal-sensing turn-on." The amp turns on when an input signal is present. This means you don't use the ninth wire (the blue wire) of either cable for this installation.

Expert installation tip

Before you run these two 9-wire cables through your car, mark both ends of one cable with a piece of electrical tape. That way, once the cables are in place, you'll know which of those cables is for the amp inputs and which is for the amp outputs.

Some products to help you do it

Crutchfield offers a 12-foot and a 20-foot version of EFX's 9-wire cable, to accommodate different sized vehicles. We also carry a small selection of highly conductive, pure copper speaker wire, available by the foot. You can use that for connecting your amplifier to a factory system instead of the 9-wire cable, if you want. We really like the EFX cable because it's such an elegant and easy option because each set of speaker wires is color coded. 

A multi-pack of Posi-Products Car Stereo Connectors could come in handy here. You can make all the speaker connections without having to solder or crimp anything. One package will cover this job and give you a few spares.

High power amps need bigger wires

For amps with more than 75 watts RMS of output per channel, it might be better to go ahead and run new 14- or 16-gauge speaker wires directly from the amplifier to each speaker.

Factory speaker wires are very thin, with high electrical resistance. They can cause noticeable power loss when higher wattages try to get through. But amplifiers of 75-watts or less aren't really affected by this. Running their output through factory wiring remains a practical and convenient solution.

Line output converters

Another popular way to connect an amplifier to a factory radio is to use something called a line output converter. It connects to the factory radio's speaker wires and converts the speaker-level signal to a preamp-level signal. This lets you use RCA cables to run that signal to your amplifier. 

AudioControl LC6iB line output converter

A line output converter offers some advantages, like the ability to sum and control signals of a multi-channel factory system. So if you're upgrading a complex system, using a line output converter might be your best option.  The speaker wire solution we've shared here is a simpler, less-expensive alternative that will work for most people. Read more about line output converters. 

Let us know what you need

This article focused on a way to simplify the speaker connections. For information about other aspects of amplifier installation, like power and ground wiring, check out our Amplifier Installation Guide.

If you have any questions about connecting a new amplifier to your speakers, contact our advisors via chat or phone. They'll take the time to answer your questions and explain the details, then get you set up with whatever you need.

  • Damian from Calgary

    Posted on 11/26/2018

    Hi Buck. 2010 Mazda 3 w/ 6 speaker non Bose. Upgrading by adding new Component (~75 RMS) and tweeter set to front and new 8" sub (~ 250 RMS) in trunk. Leave or remove factory rear speakers for now. Looking at Speaker Level connection to OEM head unit to 4 channel amp. 2 channels for front and bridge 2 for sub. QUESTIONS: Can i still somehow wire in my rear speakers Without the amp? Which line do i run in for the amp signal? At 75 RMS, im on the cusp of the 18 gauge EFX 9 wire suggestion. Is it worth the cost and effort to go thicker? Thanks a ton for your time and input. Cheers.

    Buck Pomerantz from Crutchfield on 11/27/2018
    Damian, You can leave your rear speakers hooked up to the receiver's speaker outputs. Use the front speaker wires, front left and front right, for your amp's inputs and outputs. The 18-gauge 9-conductor cable will work just fine.
  • Sam Raj from Jacksonville Florida

    Posted on 11/24/2018

    I have 2017 honda accord lx. It has only four speakers. I would like to upgrade them, please suggest brands. Secondly, what can i do to add a small amp to stock head unit. I just want a little bass and clear sounds. If i dont choose an amp, could you point me to a great 2way or 3way for my accord. I have been lurking your website for months to upgrade my stock system and you provide DIY instructions perfectly. Thank you in advance.

  • Sebastian from Compton

    Posted on 11/21/2018

    Hi, I recently installed a 4 channel JBL GX-A604 amp into my 2018 honda accord, also I upgraded the factory speakers with 4 JBL cs763 3 way speaker. The amp has high level input plugs built in. I didn't want to cut any wires so I ran 16gage speakers wires from the speaker to the amp input back from the amp output to the speaker. Everything works just perfect, but the only problem is when I turn on the car I can hear a high frequency noise that increases with the RPMs of the car. any ideas how to fix this problem? Thanks a lot

    Buck Pomerantz from Crutchfield on 11/23/2018
    Sebastian, The noise you describe is usually caused by a loose or bad ground or power connection. Tighten and secure all connections. Make sure the ground connection is metal-to-metal with any interfering paint scraped off.
  • Ciprian from Bucharest

    Posted on 10/30/2018

    Hi there. Can you please help me with an example of an amplifier that can support 4channel input and 4 channel output in terms of wires? Most amplifiers have rca inputs. Thank you. Also, do you have a European distributor for your parts? Thank you !

    Buck Pomerantz from Crutchfield on 10/31/2018
    Ciprian, Check out this Pioneer GM-A4704. If you look closely, some of the photos show the speaker-level input harness connections, where you use an included harness attached to speaker wires coming from the radio's output. Many other amps feature similar connections. I don't know what products are available in your country (Crutchfield is only licensed to sell gear in the United States and Canada) but a web search for car audio in your city should come up with a few possibilities.
  • James Carr from Lexington

    Posted on 10/19/2018

    2005 Chevy Suburban with Boise system and amplifier trying to run a line out converter for RCA what wires are my speaker wires for the front I mean for the back and where do I run my remote wire to what wire on the back of the factory day

    Buck Pomerantz from Crutchfield on 10/23/2018
    James, It looks like the best location to get full-range speaker-level signals for your line output converter's inputs are the rear door speakers. A great way to get a remote turn-on signal is to use an Add A Fuse connector plus a 2A to 10A fuse in your vehicle's fuse box attached to a 12-volt circuit that is only on when the vehicle is on.
  • Eric from Houston

    Posted on 8/9/2018

    Plan on using the 9-wire EfX to install/connect an Audio control LC4-800 to stock deck in 2017 F250 without Sony premium. No wiring harness available yet. Will that EFX wiring support the 125 RMS from the LC? Or should I go with something bigger?

    Buck Pomerantz from Crutchfield on 8/13/2018
    Eric, That 18-gauge wire will work well for the amp's input connections, but may restrict that much output power. It'll work, but you'll get better results running larger, 16- or 14-gauge, wire from your amp to each speaker.
  • Buck Pomerantz from Crutchfield

    Posted on 6/1/2018

    Manoj, I don't know what kinds of wiring and connectors are available in your country. It sounds like you should visit a car audio dealership and hire them to install your amp and sub.

  • Manoj Kumar from Riyadh

    Posted on 5/30/2018

    Dear Support, I have booked a Honda Amaze car in India which comes with all in one head unit(builtin navigation, radio,reverse parking camera view Etc.) So that I don't wanted to replace head unit. I have an 'Alpine MRV-F300 4-channel Amp and a Alpine PWE-V80 (Under seat Sub). Please let me know what are the accessories I have to buy for connecting these two amplifiers with my factory head unit? I'm looking forward to Ur kind support.Thanks

  • Buck Pomerantz from Crutchfield

    Posted on 5/25/2018

    Saul, Crutchfield's Vehicle Guide shows that your Acura's 7-speaker premium sound system actually consists of ten separate drivers: 2 tweeters, 2 woofers, and a center channel up front; two full-range speakers in the rear doors; 2 full-range speakers in the rear deck; and a subwoofer back there as well. Each one of these is powered by a separate channel of the factory amplifier. It sounds like you should call Crutchfield and talk to an Advisor who'll have all the information necessary to help you get great sound in your car with some aftermarket speakers.

  • Saul from Sylmar

    Posted on 5/24/2018

    2017 ILX premium ( 7 speakers; including a factory 8" subwoofer). I want to switch all front and rear factory speakers including the sub, the car does come with a factory amp. (Which by the way the speakers are a joke) . I want a little more thump without messing with the infotainment system. Factory amp is @ 4ohm , i'm sure it's 4 channel. Can I add a better amp , leaving the factory wiring alone?

  • Buck Pomerantz from Crutchfield

    Posted on 5/21/2018

    Daniel, Without knowing precisely what your amp is and what its input connections are, no one can say which setup would be better. From the wiring kit's point of view, you'd be ruining a perfectly good RCA cable instead of using speaker wire. But if your amp allows high-level input through its RCA connections, then you might as well cut connecters off and tap the bare wire-ends to the factory speaker wiring.

  • Daniel Nelson from Everett

    Posted on 5/16/2018

    Question: Seen there is a caution in the EFX Amplifier Wiring Kit 4-gauge w/Patch Cord manual that is confusing to me. Manual says CAUTION: If your stereo does not have RCA outputs, do not cut off the ends of the Scosche audio cable and connect/splice them to any speaker wires!!! You will need a line output converter to convert the speaker wires of the stereo into RCA line-level outputs. In my case I am using speaker level reference inputs to my infinity amp from my car's OEM HU with no RCA line outs. Would using the spliced RCA cables be better then plain wires in bring the speaker level signals out to the amp? They sure would be easier to connect RCA plugs on the amp side. Also since I am using speaker level inputs, the line output converter is not needed, it is already in the amp. Please advise, Thanks.

  • Buck Pomerantz from Crutchfield

    Posted on 4/24/2018

    Pete, I don't see why not. Although you might get better results using a line output converter with bass restoration, like an AudioControl LC7i, which also has all the inputs and outputs you'll need.

  • Buck Pomerantz from Crutchfield

    Posted on 4/24/2018

    Jay, A flickering receiver could be caused by a loose wire or the electrical system being overwhelmed by the amplifiers' appetite for power. If you bought any of your gear at Crutchfield, you could call Tech Support for free help troubleshooting your system. Their toll-free number would on your invoice. If you purchased your equipment elsewhere, you can still get expert Crutchfield Tech Support - 90 days-worth for only $30. Click on this link for details.

  • Pete Godwin from Pemberton

    Posted on 4/22/2018

    I am attempting to connect an Alpine ktp445-U anplifier to my factory stereo using speaker level inputs on the amp. I would also like to add a powered sub in the future and still maintain the factory radio. Can the same wires I'm using for the inputs on the alpine amp be used for the subwoofer also? Or would I need a 5 channel LoC for that?

  • Jay from NPB

    Posted on 4/22/2018

    Hello Mr.Pomerantz, also wanted to note that I know it's not a scratched C.D. because although the high frequency skips happen in the same places, like the first of the 3 loud crashes in Rush's YYZ, at volume aren't present when volume is lowered to the 14 level area, and happen while idle/not moving - all connections are tight. Any help will be greatly appreciated, Jay.

  • Jay from NPB

    Posted on 4/22/2018

    Hello Mr. Pomerantz, I just installed a Pioneer AHV-200E H.U., Axcess steering wheel control module, Metra wire harness's, (1) Sound stream ST. 700D mono sub amp, Sound stream ST4 1200D, Pioneer 8" 150w RMS/300w Max. subs, (2) 75w RMS/225w Max. Infinity Kappas, (2) 30w RMS/60w Max. 2.75" OEM Jeep speakers, (2) 45w RMS/90w Max Infinity .75" tweeters, 1 Farad capacitor, and already have 160A alt. and a glass mat battery. I replaced the 700D with a 1000D mono sub amp only after 2 weeks because it was overheating - (cutting out for a few minutes before coming back on- protection mode) - I like it LOUD and listen to classic/hard rock. After installing the new 1000D it sounded great for the first few days - tight kick drum and warm punchy bass (*as per your installation tutorials). Then I discovered all the H.U. cross overs and the sound really came to life, but now my system is cutting off for .5 - 1 sec. on certain high notes when volume cranked 20-25 out of 40. I can still hear the subs but faintly when this happens and I have even caught the H.U. "blinking" flickering at me for .5 - 1sec. I have shut off HPF/LPF on the H.U. using the amps settings and it still happens. I have raised the LPF & lowered the HPF all the way on front/rear ch.'s of the 1200D amp in order to use the H.U.'s settings @ LPF =200Hz, HPF = 225Hz at 6 dB and it STILL happens. It sounds GREAT at vol. 25 with no distortion, but just cuts off, unless I turn it down to 14. I hope you can help me, Jay.

  • Buck Pomerantz from Crutchfield

    Posted on 4/19/2018

    Joe, Amplifiers that have speaker-level inputs have LOCs built in. There are no specific harnesses made for this application, but we sell the 9-conductor cable and connectors so you can make your own.

  • Joe from Greenbelt

    Posted on 4/19/2018

    I have a factory head unit on my Tacoma 2015 its a non JBL, if I get a amp with speaker level inputs will I need a LOC? Do you supply a harness for this

  • Buck Pomerantz from Crutchfield

    Posted on 4/16/2018

    Mickey, As far as I can tell, the preamp outputs will be live when using speaker-level inputs.

  • Mickey Akins from Portland

    Posted on 4/15/2018

    If i use the 9 wire for connecting my pioneer 4 channel amp; will the rca bypass from that amp still be able to be used for connecting to my mono pioneer sub amp?

  • Buck Pomerantz from Crutchfield

    Posted on 4/9/2018

    Kevin, If you're just adding a subwoofer to a factory system you can tap the rear speaker wiring for inputs. Otherwise, this wiring technique described in this article doesn't apply to systems with a factory amplifier.

  • Kevin from Essington

    Posted on 4/5/2018

    Can't I just tap into the rear door speakers for signal and leave the factory speakers alone ? Will the high level inputs be affected by the factory amp?

  • Buck Pomerantz from Crutchfield

    Posted on 3/21/2018

    Michael, AudioControl's LC7i line converter has AccuBASS bass restoration onboard, so there's no need to add an Epicenter to the system.

  • Buck Pomerantz from Crutchfield

    Posted on 3/21/2018

    David, I'm not sure what you're intending, but the eight conductors should never be connected together. This article and illustration describe how to hook speakers up to an amp that has speaker-level inputs. You may need to use a line output converter to use this wiring technique.

  • Michael from Hampton

    Posted on 3/21/2018

    I am installing 2 amps one for a subwoofer and a 4 channel for the door speakers. I have a lc7i lone converter. Would a epicenter help with the subwoofer and would I hook up the epicenter to the lc7i? Or would just running it with the lc7i be good enough without an epicenter? The 2 amps are Rockford 400a4 and a bd1000a1.

  • David from Seattle

    Posted on 3/17/2018

    So with the 9-wire, i cut and attach 8 of one end into the respective speakers from the radio wire harness, and the other end? do i roll all 8 together and attach that to the input at the amp where the blue wire would normally go? The amp i have has RCA input jacks.

  • Buck Pomerantz from Crutchfield

    Posted on 3/7/2018

    Chris, In order to connect your Epicenter to a factory stereo will probably require a line output converter. And if your 4-channel amp doesn't have speaker-level inputs, it'll need one as well. Why don't you give us a call so an Advisor can help you get all the gear you need for a successful install.

  • Chris from Los Angeles

    Posted on 3/6/2018

    I have 2 amps (1 bass, 1 voice 4 channel) and an epicenter I would like to connect to my factory stereo. What would I need? A convertor or?

  • Buck Pomerantz from Crutchfield

    Posted on 3/6/2018

    Christopher, The second diagram of this article might help visualize what you want to do. In your case, with only a single speaker wire to tap into, you either tap the speaker wires twice, for the positive and negative left and right inputs, or just use one input.

  • Christopher Amerally from New York

    Posted on 3/2/2018

    I have the new JL Audio RD 500/1 amp. I purchased this amp cause it doesn't require a line out converter. I am still alittle confused as to how to install it correctly can you help me out. My goal is just use the factory oem subwoofer wire to tap into for signal to that amp via the JL Audio rca to speaker wire. The amp also comes with signal sensing no need for the blue wire. How to set it all up is what I need help with

  • Buck Pomerantz from Crutchfield

    Posted on 2/16/2018

    Ty, One of the 9-conductor cables goes to the amp's speaker-level inputs, and the other goes to the amp's outputs.

  • Ty Weber from Dodge City, KS

    Posted on 2/14/2018

    so then where do you put the 9 wire cables in to the amp.

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