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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.

  • 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).
  • Hannad Eid

    Posted on 5/6/2022

    I am trying to amp only the door speakers in my fj cruiser with a 2 channel amp. When i disconnect them from the radio the tweeters in the dash and the front speakers don't work only the headliner speakers work. What should i do

    Commenter image

    Buck Pomerantz from Crutchfield

    on 5/6/2022

    Hannad, Perhaps you missed the section of the article that reads: "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."
  • Johnny King from MERIDIAN

    Posted on 1/11/2022

    Thanks for the read

  • Christian

    Posted on 1/10/2022

    Thank god. I watched hours of tutorials on youtube for a trivial information, namely where the output from the amp enters; in the head unit or towards the car. Thanks for the simple explanation given

  • Joe from Ewa Beach Hawaii

    Posted on 12/31/2021

    I have a 2002 Subaru Impreza and I splice my stock radio and speaker wire with the 9 wire harness without making the "t- harness" connecting it to the high input on my a6004 Jbl amp and it's working fine my question is do I really have to do the "t-harness" method instead of splicing it all together? I hope you understood that lol

    Commenter image

    Buck Pomerantz from Crutchfield

    on 1/3/2022

    Joe, The whole point of this wiring scenario is to send the radio output to the aftermarket amp's input, and the aftermarket amp's output to the speakers. If you connect two outputs together, as it seems you've done, one will eventually die as the two amps will be fighting each other by sending power to each other's outputs.
  • Jesse woodruff from Atwater

    Posted on 11/5/2021

    I put one in my 2916 Honda Fit it was going good for about 2 1/2 days then my radio stopped working. The red security light still blinks and the cd play ejects my cds but that's it. What can be the problem?

    Commenter image

    Buck Pomerantz from Crutchfield

    on 11/8/2021

    Jesse, It sounds like you need to install load generating devices, so your radio won't shut down because speakers aren't directly connected to its outputs.
  • Wes from Gilbert

    Posted on 10/29/2021

    Excellent article. Thanks so much for putting this out there. I do have one question. I have a 2021 Jeep Grand Cherokee with the factory 6 speaker system and head unit. I'm looking to add an aftermarket amp and to upgrade the existing speakers (no sub). This article describes how to integrate the factory wiring with the amp, but I have read that would need to also need add load resistors between the positive and negative speaker connections to ensure that the head unit communicates properly with the speakers. Is this true for my car?

    Commenter image

    Buck Pomerantz from Crutchfield

    on 10/29/2021

    Wes, In Crutchfield's Vehicle Guide Research for your Jeep, there's a note that reads, "When adding an aftermarket amplifier to the factory radio, you'll need to use load resistors to keep the radio operating properly." Give us a call and talk to one of our Advisors. We can help you choose the right gear and give you the right advice on how to install it.
  • Kailer Apilado from Lihue

    Posted on 9/29/2021

    Hello, I have a 2014 Honda Accord EXL that has a factory amp in it. I was curious as how I can wire and after market amp into the car too. I believe that I can't use a LOC because of the amp. If possible could someone guide me in wiring an after market amp to power a sub when my car already has a factory amp in it and I don't want to change the stock deck. Thank you so much!

    Commenter image

    Buck Pomerantz from Crutchfield

    on 9/29/2021

    Kailer, An LOC is exactly what you can use to connect high-level, amplified signals to an aftermarket amplifier's inputs. Check out the lower diagram in this article. If your sub amp can't take that high an input, use a 2-channel LOC.

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