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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.

  • Luis ponce from El sobrante

    Posted on 12/28/2022

    2019 Honda civic sedan what harness and adapters do I need to hook a amp and 8in.woofer

    Commenter image

    Buck Pomerantz from Crutchfield

    on 12/28/2022

    Luis, As of right now, I don't see any T-harness adapters for Honda Civics. It looks like you'll have to hard-wire an LOC or an amplifier with high-level inputs into the Honda's system for your upgrade.
  • Jordan Ramirez from Parlier

    Posted on 12/17/2022

    How do I wire 4 front doors component speakers using the factory wiring to a 4 channel amp. I'm confused because I have seen a lot of people run separate speaker wires for mid and tweeter on each door but what do I have to do in order to power all 4 components with use the stock speaker harness wiring? I plan on leaving the rear speaker with stock power from the radio.

  • Brian from Lake city

    Posted on 10/19/2022

    I have the Rockford fosgate r2 500x4. 75 watts a channel at 4 ohms. Do I also add the aftermarket rms it's putting out as well I believe it's 23 watts a channel. Thanks.

    Commenter image

    Buck Pomerantz from Crutchfield

    on 10/20/2022

    Brian, Power comes from the amplifier. Your head unit's output power is not used at all in such a system. Its output power will be either disconnected or reduced to drive the amp's input.
  • John

    Posted on 10/2/2022

    Say I run my factory receivers "amplified" (20WRMS) signal though 18 gauge speaker wire to an amplifier in the trunk with a built in line out converter. Can I run my amplified 125WRMS signal through 16 gauge speaker wire for the aftermarket speakers right next to the 18 gauge (less than an inch apart) back up front to the factory speaker connection? I'm specifically concerned about any audible noise or feedback being introduced into the system from running these wires close to each other.

    Commenter image

    Buck Pomerantz from Crutchfield

    on 10/3/2022

    John, The amplified signals running through speaker wires are usually strong enough to overwhelm any radiated interference they may pick up, so placement doesn't matter as much as with line-level preamp signal cables.
  • 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.

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