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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. 

Note: This article explains how to connect an amplifier to a factory stereo system that does not include a factory amp. A Crutchfield article about connecting an amp to a factory-amplified system will become available soon.

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. 

Crutchfield 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" Crutchfield 9-wire speaker cable 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.

Something you may need

Sometimes after you cut the factory speaker wiring, the radio will shut down, because it can't detect any speakers connected to it. To solve this issue, you must install a load generating device on each output channel, so the radio will operate properly.

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

Our favorite option is the Crutchfield 9-wire cable shown above because each set of speaker wires is color coded. We also carry a selection of highly conductive, pure copper speaker wire, available by the foot, if you prefer that.

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.

PAC Audio offers a few vehicle-specific T-harnesses that'll help you add an amplifier to a select number of vehicles with non-amplified factory stereos. 9-wire cable will also come in handy for these installations, in order to connect your aftermarket amp's inputs and outputs to the system.

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.

  • Daniel B Schaut from LAS VEGAS

    Posted on 2/3/2023

    I am installing a 4 channel amp to my factory stereo. I have a 4 channel line output converter to RCA that will connect to input on amp? Than I will use 9 wire from out put to behind stereo and patch that onto newly ran 14 guage speaker wire. I already have a 15" sub and amp installed. I am just using 2 distribution blocks 1 for power and 1 for ground in back for both amps. Does this sound right? Thank you

  • Marc from Whittier

    Posted on 1/31/2023

    Hello, How does this work with a 5 channel amp? Meaning my R2-750x5 has, 4 Sub high level wires. Where do Subs wire tap in? Front speakers or rear?

    Commenter image

    Buck Pomerantz from Crutchfield

    on 2/1/2023

    Marc, If I understand your question correctly, that amplifier has an input selection switch you can set to "4" to use four inputs and create a subwoofer channel made up of a left/right signal pair. No tapping needed.
  • Caroline from Warrenton

    Posted on 1/23/2023

    If you have a speaker level input, do you run that to the speaker wires in the back of the head unit with one 9 wire? Where does the other 9 wire go and what is it for? Isn't one 9 all you need if you are using high level input on the amp? I'm confused.

    Commenter image

    Buck Pomerantz from Crutchfield

    on 1/24/2023

    Caroline, The article describes using one 9-wire cable from the factory radio's speaker wiring for an aftermarket amplifier's inputs, and another 9-wire cable from the aftermarket amplifier's outputs to the vehicle's speaker wiring.
  • Mick

    Posted on 1/21/2023

    I hope that I am missing something here, but how do you get the wires from the head unit into the amps input? does it not have to be RCA?

    Commenter image

    Buck Pomerantz from Crutchfield

    on 1/23/2023

    Mick, This article describes using 9-wire cable, not RCA cables, to connect to an amp's speaker-level inputs.
  • UnearthlyDust from Hockley

    Posted on 11/16/2022

    2019 Dodge Challenger. Factory Touch Screen, no factory amp or woofer. Just the standard 6x9 in the front and the 6.5 in the rear. I am adding a 4 channel amp for the speakers and a subwoofer amp to run some subs. I do have the Kicker Resistor I need to install. Do you recommend running the harness wires to the amps or should I get the RCA convertor and run RCA from the head unit? I heard running the 9 wires or whatever it is, will cause eng noise in the amps. Im not sure if that is true or not. Any thoughts you have, I would greatly appreciate. I am changing all the speakers to the Kicker.

    Commenter image

    Buck Pomerantz from Crutchfield

    on 11/17/2022

    Dust, Noise that changes pitch along with the engine's RPM is usually caused by a loose ground connection somewhere. I don't know what a "Kicker Resistor" is, but your vehicle's factory system includes an amplifier - even if you don't have the Alpine stereo option - and you'll need a line output converter with load resistance either built-in or as separate components in order to incorporate a new amplifier into the system. Give us a call, so an Advisor can help you get everything you need for your install.
  • Miguel Nava from Bothell

    Posted on 11/6/2022

    Great article to help audio amateur how to connect a converter. THANKS!

  • Charles from Front Royal

    Posted on 10/7/2022

    Hello, Will this work with an aftermarket radio as well? I put in four alpine type s door speakers in my truck, I have an aftermarket head unit that I am going to install that has 60 watts RMS per channel. I am planning on adding a 12 inch sub in the near future and adding an amp to power that, would I be able to connect the amp to the head unit to give a little more power to the speakers ? The front speakers are rated at 80W and the rears are 75W. I also have tweeters on the pillars

    Commenter image

    Buck Pomerantz from Crutchfield

    on 10/7/2022

    Charles, You can't add the power of two amplifiers together. When you have an aftermarket receiver, you should use its RCA outputs for your amplifiers' inputs. If you want to use the receiver's powered outputs, you'll need to reduce the signal strength so the amp's input can handle it without distorting.
  • Jeffrey Praski from Richmond

    Posted on 7/26/2022

    I am thinking of adding speakers and amp. I was going two keep factory speakers. I would splice into speaker wire; does this change the impedance? Can i send speaker level input to amp, in parallel?

    Commenter image

    Buck Pomerantz from Crutchfield

    on 7/27/2022

    Jeffrey, When you disconnect speakers from a factory receiver or amplifier, the factory system's output impedance changes radically, sometimes to infinity and the system shuts down. In these cases you'll need load resistors on the outputs to keep the signal flowing properly. Do not wire the speakers to both the factory receiver/amp and the aftermarket amp at the same time - that could lead to damage.
  • Jonathan Hernandez from Riverside

    Posted on 6/21/2022

    I installed a sub to my factory stereo using an interface adapter a while ago. Recently purchased a 5 channel amp to amp the door speakers too. I already have RCAs coming out of the factory stereo into the amp. Do I need to tap into the stereo harness to amp the door speakers? What options do I have?

    Commenter image

    Buck Pomerantz from Crutchfield

    on 6/21/2022

    Jonathan, Give us a call, so an Advisor can help you figure out what interface adapter you have, how it's hooked up, and why it doesn't already have connection options for another amplifier.
  • Don

    Posted on 6/14/2022

    I have a factory stereo, added an amp and new speakers. I got a LOC and not sure if I did it right. Do I cut the factory speaker wires, hook them to LOC, run the RCA cables and thats it? Or do I run new speaker wire from speakers to the AMP as well. Right now I spliced the LOC into the factory speaker wire and only ran RCA cables. Amp has nothing hooked up where you run speaker wires.

    Commenter image

    Buck Pomerantz from Crutchfield

    on 6/15/2022

    Don, Like this article indicates, if you cut the wiring harness and run, via speaker wire, to an LOC - and then by RCA to the amp - you'll need to then run speaker wires from the amp's outputs back to the wiring harness and connect to the wires that go to the speakers (the other side of where you cut the harness wires).

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