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Connecting your car speakers to an amp

Tip: You can use your vehicle's factory wiring

Installing an amplifier

Sending the audio signal from a receiver to a 4-channel amplifier's inputs via RCA cables or the amp's speaker-level inputs is straight forward and simple enough, but getting the amplified signal back to the speakers—well that's another matter.

This article discusses adding an amplifier to an aftermarket stereo. For tips on connecting an amplifier to a factory stereo, read this article instead.

Getting signal to the speakers

The speakers are usually in four different corners of your vehicle, and running separate new speaker wires to each one presents many challenges, including how to get the wire past the car door hinges to the front door speaker locations.

A convenient way to send the powered signal from your amplifier to your speakers is to run the speaker wires back to the harness behind your stereo, where all your car’s speaker connections are accessible in one place.

Which speaker wires go where?

Normally, when you install a new stereo, all the wires from the stereo would connect to the car wiring adapter. The wires would run from one black connector to the other (the right side of the photo below).

But since we're using an external amplifier for the speakers, the speaker wires from the car get diverted to the amp — that's the bundle of wires on the bottom plug heading left to the amplifier.

The speaker wires from the new stereo aren't used. You can either cut them off (like we did in the photo below) or just tape them up – each wire individually – so that none of the wire ends can touch anything else.

Meanwhile, the RCA cables carry the audio signal to the amplifier and the blue wire from the stereo turns on the amp whenever the stereo is turned on. And yes, fade and balance controls will still work fine, so long as you connect the RCA cables correctly.

amp wiring example

Running the amp's output wires to the speaker wires on the stereo's adapter harness is how you avoid having to run new speaker wiring throughout the car. That's the bottom side of the triangle in the photo above — speaker wires from the amp connect to the speaker wires on the adapter harness. Then that harness plugs into your car. The diagram below is a more detailed depiction of the layout.

multi-conductor cable diagram

New speaker wires from the amp connect to the speaker wires in the stereo adapter harness

For 4-speaker systems, you'd need to make eight connections — a positive and negative wire for each speaker. This means, you just need to run the eight speaker wires from the dash to the amplifier, just like you do the RCA cables. In fact, when you're installing the amp, it's smart to run the RCA cables and new speaker wires at the same time.

Crutchfield 9-wire Ultra Flex speaker wire

Some products to help you do it

Our favorite option is the Crutchfield 9-wire cable shown above because it helps simplify running eight speaker wires plus a remote turn-on lead from your amplifier to the rear of your receiver and each set of speaker wires is color coded. We also carry a small selection of highly conductive, pure copper speaker wire, available by the foot, that will also work well, if you don't want the 9-wire, all-in-one solution.

A multi-pack of Posi-Products Car Stereo Connectors could come in handy here, so you can make all the speaker connections without having to solder anything.

High-power amps need bigger wires

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

Factory speaker wires are very thin, with high electrical resistance, so 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, so running their outputs through factory wiring remains a practical and convenient solution.

Let us know what you need

This article focused on a way to simplify the speaker connections when using an aftermarket stereo. If you're connecting an amplifier to a factory system, check out this How To guide for tips. 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.

  • Chris Reynolds from Cutler

    Posted on 9/18/2022

    I got this PAC-RP4-FD11-Wiring-Interface with the ready harness. I am now wanting to install a 4 channel amp to power my 4 door speakers which i upgraded to kicker in my 2010 ford f150. How can i run the speaker wire from the amp and still be able to pick up my phone call audio through the speakers?

    Commenter image

    Buck Pomerantz from Crutchfield

    on 9/19/2022

    Chris, That harness is for replacing the factory receiver and I can only assume it will retain all factory functions like hands-free calling. This article explains how to wire your aftermarket amp's outputs to the speakers via the vehicle's factory wiring. If re-reading the article doesn't help, perhaps you should take your vehicle to a professional car audio installer. It may be that you'll need an additional vehicle-specific harness to bypass the factory amplifier.
  • Jamar winn from Baltimore

    Posted on 8/4/2022

    When running speaker wire from the amp for the for speakers can you militarysplit the wires into wires from the headunit

    Commenter image

    Buck Pomerantz from Crutchfield

    on 8/5/2022

    Jamar, No you should not do that. When powering speakers from an amplifier, you need to disconnect them from the receiver. Otherwise, the amp and receiver's outputs will fight each other and possibly destroy themselves.
  • Omar Salameh from Jacksonville

    Posted on 7/12/2022

    I have been trying to run a 4 channel amplifier to my door speaker wires behind the aftermarket radio. Keep in mind I have installed many subwoofer amplifiers over the years but for some reason my 4 channel amp [I have tried 2 different amps] won't stop clipping and sounding terrible. I have run RCA jacks to the proper places I'm not Sure what I'm doing wrong please help

    Commenter image

    Buck Pomerantz from Crutchfield

    on 7/14/2022

    Omar, It sounds like you might benefit by checking out How to set amp gain, to cure your distortion issues.
  • Brad james from Richmond

    Posted on 7/2/2022

    We're do the rca go if I have a 4 channel they go from aftermarket radio too amp I have an android radio with many rca outputs on the back

  • Daquavis from Plano

    Posted on 4/24/2022

    So I have the Bose system in my Tahoe non lux , I've ran the 9 wire without connecting to pioneer head unit but to metra harness.. I'm using a PAC to retain functions.. am I doing this correctly or am I missing something? I have image dynamic 6.5 in all doors also if that helps. I only ask because local shop wants $755 to install head unit even if I ran my own rca's & 9 wire throughout for amp. Seems like a ripoff!

    Commenter image

    Buck Pomerantz from Crutchfield

    on 4/25/2022

    Daquavis, If you have the skills to install amp wiring correctly and neatly, there's no reason you couldn't install a receiver yourself. It sounds like the installer expects to have to integrate with your aftermarket wiring as well as add in a new receiver, harness, and interface.
  • Shawn Morales from El Paso

    Posted on 4/20/2022

    So even if my aftermarket radio has 4 channels, would I need a 6 channel amp for six speakers (front and rear door, along with rear deck) or would I splice into let's say the rear door for the rear deck if I had a 4 channel amp?

    Commenter image

    Buck Pomerantz from Crutchfield

    on 4/22/2022

    Shawn, You can power your six speakers with a six-channel amp, or with a 4-channel amp using the rear door and rear deck speakers wired together, in parallel (positive to positive, negative to negative). That way, the amp will put out about twice the power per channel, because the loads have been reduced to 2-ohms - and divided into two speakers will put out the same power per speaker as the non-combined channels.
  • Francisco Quinones from New York

    Posted on 3/31/2022

    Hi, If I want to run my speaker wires from the amp to my pioneer aftermarket radio do I connect the wires to the after market harness or directly to the radio harness and not use the after market harness?

    Commenter image

    Buck Pomerantz from Crutchfield

    on 4/1/2022

    Francisco, You'll use RCA cables to feed signal from your aftermarket receiver to your aftermarket amplifier. and then speaker wire from the amp to the speakers via the vehicle's harness - what you're calling "the radio harness."
  • Rynne Bagguley from Oxford

    Posted on 12/31/2021

    Would I still be able to run a aftermarket amp for subs even if the wiring harness sent with the aftermarket radio doesn't have a remote wire?

    Commenter image

    Buck Pomerantz from Crutchfield

    on 1/3/2022

    Rynne, You can run a remote turn-on wire from a switched circuit in the car's fuse box, if you can't find one anywhere else. Most aftermarket receivers, however, do have a remote turn-on circuit that you can tap into.
  • Artur from Denver

    Posted on 12/18/2021

    Thanks for the article Buck. In it, you state that above 75rms you will start experiencing power loss, but also replied to someone's question telling them they should be good to handle up to 200rms. I have a '22 Santa Fe with 630 watt Harmon/Kardon 12 speaker system (including a set of 2-ways in the rear doors and sub) I'm looking to upgrade. I plan on running around 100-140 rms per speaker. Realistically, would it be worth re-wiring with 14 or 16 gauge? Or would the extra work create a negligible improvement in quality. Thanks!

    Commenter image

    Buck Pomerantz from Crutchfield

    on 12/20/2021

    Artur, Our service techs have never heard of anyone having issues using factory wiring for their aftermarket amplifiers. But it certainly won't hurt anything to upgrade your wiring.
  • Felix from Yuma

    Posted on 12/2/2021

    At what RMS power would you recommend running new speaker wire?

    Commenter image

    Buck Pomerantz from Crutchfield

    on 12/2/2021

    Felix, Your vehicle's wiring can probably handle up to about 200 watts RMS per speaker. More than that, and you might consider upgrading the speaker wires.

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