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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.

  • Don

    Posted on 9/19/2021

    I am putting in a Line Output Converter to my factory HU. I'm tapping into the speaker harness on the one end of LOC and then running RCA cables to amp from the other end. Do I still have to run speaker wire to the Amp? Or does the RCA cables serve that purpose?

    Commenter image

    Buck Pomerantz from Crutchfield

    on 9/21/2021

    Don, The RCA cables carry the input signals to the amplifier. Then, the amplifier's output signals must travel through speaker wires from the amp's outputs to each speaker. Like the article shows, you can use 9-conductor cable to connect the amp's outputs to all the speakers via the factory speaker wiring found behind the factory radio.
  • Julio from Costa Rica

    Posted on 9/13/2021

    I have a BMW e46 and the speakers are connected to an amp, but they don't sound pretty well, I changed all the speakers and the car sounds like garbage, is there something you recommend to check that might be the problem?

    Commenter image

    Buck Pomerantz from Crutchfield

    on 9/13/2021

    Julio, Unfortunately, a lot of premium factory car audio systems come tuned for cheap factory speakers with no fullness to the sound. Pretty much the only way to combat this is to use a DSP, digital signal processor, to upgrade the factory sound for new speakers and amplifiers.
  • Ian from Beulah

    Posted on 9/2/2021

    Hello, if I buy a new set of speakers 50RMS, will I have to use a channel on my amp to power them? or could I just drop the speakers in and not mess with the speaker wires?

    Commenter image

    Buck Pomerantz from Crutchfield

    on 9/3/2021

    Ian, A speaker must be connected to wires coming from an amplifier's output to work. That amp could be inside a receiver or be a separate unit. Without knowing exactly what vehicle, amp, or speakers you're talking about, we can't help you with wiring advice. With questions like this, it's always better to have a conversation with a real live human. 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.
  • Oshin from Los Angeles

    Posted on 8/5/2021

    This is super helpful Buck, thanks for sharing. I was wondering, however, how I'd tap into my factory harness if the car has a (relatively weak) stock amp that I plan to upgrade. I was planning on upgrading to a newer, more powerful aftermarket amp using a vehicle specific line output converter that comes with its own harness and which would connect to the aftermarket amp with 4-channel RCAs. But then I'm not sure how the amplified signal would get from the aftermarket amp to the speakers. If I were going to tap the harness as this article suggests, would I tap the harness at the point after it connects to the LOC and "returns" to the stock amp? Or the one in the head unit? Thanks!

    Commenter image

    Buck Pomerantz from Crutchfield

    on 8/5/2021

    Oshin, You could use 9-wire speaker cable to connect your amplifier's outputs to the speakers via the vehicle harness behind the radio. Cut and cap off each wire from the receiver's output and connect the amp output wire to the speaker wire running to the speakers from the harness.
  • Felix o Martinez from Vadito

    Posted on 6/4/2021

    I'm getting ready to install a blue tooth smp in my 92 jeep yj. Earlier today I was quoted 400.00 to wire my amp. I was responsible for installation. 400.00 dollars to run some wires? Thank you so very much!!!! Your sight is the easiest to follow and understand.. I will follow it and complete the installation. With peace mind thst it was done correctly. Thank you.

  • Tommie Brown from St Louis Park

    Posted on 5/21/2021

    I have a 2005 Chevy Impala 3.4. I have a aftermarket radio, new amp, and I replaced all of the speakers. Unfortunately, I bought 3 different harnesses and none of them work. I decided to disconnect the factory amp. I haven't did anything else yet. I just want to know which wires from the factory amp do I connect to my new amp? I was going to connect my rear speakers, and tweeters directly to my aftermarket radio. I just need a little more Advice.

    Commenter image

    Buck Pomerantz from Crutchfield

    on 5/24/2021

    Tommie, One of the benefits of talking with a Crutchfield Advisor when buying gear is that you'll get accurate and useful information about what accessories and wiring harnesses will be required for a successful installation. It sounds like you need a factory amplifier bypass harness as well as interfaces to whatever aftermarket receiver and amp you have.
  • James from Portland

    Posted on 4/30/2021

    What is your assumption regarding the stock speaker wires? If yheyvare only 20 or 22 awg would that change your position regarding using them for a 50 rms / channel amp?

    Commenter image

    Buck Pomerantz from Crutchfield

    on 5/3/2021

    James, Factory speaker wiring will have no problem passing that amount of power.
  • Sam from Pittsburgh

    Posted on 2/14/2021

    Hi Buck! I recently got an Infinity Primus 6004a amp to add to my 2018 Mazda 3. Can I still use the factory wiring in this case or should I run all new wire? I'm also adding Infinity Primus and Reference speakers.

    Commenter image

    Buck Pomerantz from Crutchfield

    on 3/24/2021

    Sam, You can go ahead and use factory wiring from that amp to the speakers.
  • William

    Posted on 1/20/2021

    I can't find which wire is my speakers wire behind my head unit and I'm trying to run the wire to my IC2i pro can i just use the door speaker and run a wire from that speaker to my IC2i pro?

    Commenter image

    Buck Pomerantz from Crutchfield

    on 1/25/2021

    William, Yes you can. People often use their rear speaker wiring for this connection option.
  • Trent from Minnesota

    Posted on 1/18/2021

    What would be the best way to power 6 speakers 4 6 1/2's and two 6x9s two out of the 4 6 1/2 are powered by a stock amp that I think would be best to bypass and then run all the speakers on one amp if possible. I have a aftermarket head unit and the speakers are aftermarket as well the vehicle is a 1999 chevy Tahoe LT 4 door the speakers cut out and distort when I turn the volume up over 3/4 so I'm thinking more power would help any info is greatly appreciated

    Commenter image

    Buck Pomerantz from Crutchfield

    on 2/2/2021

    Trent, The best way to figure out what'll work for you is to call us so an Advisor can help you choose the right stuff.