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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.

  • 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.

  • 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.

  • 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 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.

  • 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 3/7/2018

    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.

  • 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.

  • 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.

  • 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.

  • 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.

  • 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 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.

  • 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 4/16/2018

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

  • 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 4/19/2018

    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.

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