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Adding a stereo to a vehicle with a factory amp

Should you bypass the stock amplifier or use it?

Dave connects the new receiver wiring harness

In a Nutshell

Many of today's vehicles have an external amplifier connected to the factory stereo system. This amplifier is designed to make cheap factory speakers sound better. But it doesn't do you any favors when you replace the stereo or those stock speakers. 

Retaining the factory amp usually makes it easier to install a new stereo, and in some vehicles that's your only option. But your new stereo's sound is limited to what that amp can do. 

Bypassing the factory amp takes a little more work because you have to run the bypass harness to the factory amp, which is often located in some other part of the car. It's usually worth the extra effort because you'll get better sound from your new stereo, even if you're keeping those factory speakers. 

Full Story

While planning an article about a DIY car audio system, we came across an unexpected opportunity to showcase a question that our Advisors answer regularly here at Crutchfield:

"Should I keep the factory amp or should I bypass it?"

Many vehicles include an external amplifier as part of a factory audio system. In many cases, we'll have a wiring solution for a vehicle that either works with the factory amp or bypasses it. So, which way is better? We decided to compare both options and hear for ourselves. 

JVC KW-R925BTS CD receiver in car

We chose the JVC KW-R925BTS CD receiver for the features Dave wanted, including preamp outputs that worked with the amp integration harness.

A willing car audio test subject

Dave, one of Crutchfield's editors, wanted to replace the factory sound system in his family's 2002 Toyota Highlander. A couple of us on the car writing team got together, researched Dave's vehicle, and recommended the JVC KW-R925BTS CD receiver and JVC speakers to meet his requirements for the new setup.

We noticed that the stock system in Dave's Highlander included a factory amplifier, and Crutchfield offers ways to either integrate or bypass the factory amp in this Toyota. We decided to use this opportunity to test our theory that it's always better to bypass the factory amp. We connected Dave's new stereo both ways to see what really sounded the best.

Setting the stage with new speakers

Dave changed out the speakers before installing the new stereo so they'd be ready for the test. The right pry tools and comprehensive Crutchfield MasterSheet™ instructions led him through the procedure, and once he had the first door speaker done, the others went smoothly.

Dave replaced the front speakers with JVC CS-DR1700C 6-3/4" component speakers up front, using a universal backstrap to make a bracket for each tweeter. JVC CD-SR1720 6-3/4" 2-way speakers mounted directly into the factory brackets in the rear doors.

Wiring on back of receiver

To use the amp integration adapter, Dave plugged the adapter's RCA plugs into the JVC receiver's preamp outputs.

Getting the new radio ready for the test

To install the JVC radio, Dave began by securing the Toyota-specific kit that Crutchfield offers to the radio chassis. He also ran his Bluetooth® microphone cable from the cavity to the dashboard. Once the radio was secured with a few screws, it was time to move onto the wiring.

Dave thought that wiring to the existing factory amp in his Highlander would be fine, since it still worked. The installation would've been a little easier, since he didn't have to run any cables to the amp location. Retaining the factory amp meant he could connect the new stereo to the plug in the dash cavity, where the old radio had been plugged in.

Here's where we chimed in, explaining that Dave could expect better sound by bypassing that factory amp and directly feeding the JVC receiver's power to his new speakers. Keeping the factory amp in play would negate many sound attributes his new stereo offers.

plugging in the amp

Easy access to the factory amp's plug enabled us to test both methods.

Switching between the bypass harness and the integration adapter

We had easy access to the wiring harness that connected to the factory amp in Dave's Highlander. So we helped him wire the radio in a way that safely let us switch between the amp integration and bypass setups to compare the sound. 

Amp diagram

To use the bypass harness, Dave simply unplugged the cable from the factory amp and plugged it into the harness's plug.

How did it sound?

To put things in perspective, Dave works primarily on the home audio side of our business, so he's been exposed to some of the best sounding home audio systems out there. Here are his thoughts on the two methods of connecting his new car stereo:

"At first, I thought I wanted to use the factory amp for more power and better sound. It also looked like an easier installation, since I didn't have to get to the amp. With the amp integration harness, the sound was better than what I was used to. It had a lot more detail than the factory radio and speakers did."

So, he heard some improvement in the sound when he kept the factory amplifier in the system. Even going with the easier installation, his music would benefit. But then we moved on to the second part of the experiment:

"There's that missing bass... Bypass it is!"

"However, when the bypass was connected, I exclaimed 'Ah, there's the missing bass!' Bypassing the factory amp returned the low end that had been missing on the first go-round. The middle and high frequencies were also much more natural without losing the detail. It was a huge difference. Bypass it is!"

Factory amps can also include factory frequency settings

It's not just about the power. The factory amp can also include a filter or crossover network for specific frequencies that may not sound optimal with a new system. By bypassing the factory amplifier and feeding the JVC receiver's power directly to the speakers, Dave also bypassed any filters in the factory amp, sending a pure, full-range signal to the speakers.

Occasionally, we may not have a specific bypass harness available for a vehicle. But if you don't mind splicing some wires, you can use a speaker-wire bundle, like the EFX 9-wire Ultra Flex speaker wire bundle, to reach the output section of your factory amp.

Running wire

There it is! The Toyota's factory JBL amp is mounted under the rear seats. It doesn't have to be removed to be bypassed, which saves some time.

Installing the bypass harness in the vehicle

Once Dave decided to stick with the improved sound from the bypass adapter, he had to route the adapter's wiring to the factory amp, which is located under the rear seat in the Highlander. He found this wasn't as hard as he initially thought.

He fished this wiring bundle from the radio cavity, under the glovebox, and behind the kick panel trim on the passenger's side of his vehicle. Dave removed some of the door threshold trim, which revealed very handy channels that accommodated his wiring nicely. He neatly hid all the wires under the trim and plugged this bundle into the connector that plugged into the factory amp.

running wire

Dave ran the bypass harness from the dash cavity to the factory amp location, using the vehicle's trim to conceal the wiring bundle.

Final thoughts

Dave did a final sound check, making sure everything was working properly before replacing all the trim pieces. The new stereo system makes his family driving duties much more fun. By bypassing the factory amplifier, the music sounds more detailed and clear than it did when he used the amplifier integration harness. Whenever there's one available, we recommend bypassing the factory amp to get better sound.

If you're considering a new stereo for your vehicle, keep this option in mind. Our OutfitMyCar™ tool will show you the connection options for your vehicle. And if you have any questions, we're available via phone, chat, or email to help. 

Dave in his car

Dave's new sound system puts a smile on his face.

  • Marlon

    Posted on 7/31/2016

    I have a 2004 Toyota Sienna with the factory JBL amplifier that has a factory subwoofer. If I bypass the factory amp, I assume the factory subwoofer would no longer work? I am contemplating bypassing the amp or not. I don't plan on replacing any of the factory speakers or the subwoofer. If I should integrate with the factory amplifier, would there be an downside with sound quality with an aftermarket head unit?

  • Dave Delamere from Crutchfield

    Posted on 8/1/2016

    Marlon, the factory subwoofer would be lost if you bypass the factory JBL amplifier. While it's usually an easier installation, the downside is that the factory amp may have some frequency filters that you cannot adjust. The bypass option gives pure, unfiltered audio to work with. Also, you won't be using any of your new car stereo's power. You'll get the power from the JBL amp.

  • Mike from Boston

    Posted on 2/13/2017

    I have an 05 Tundra, I installed a Kenwood radio in it. My tweeters in the front don't work right now and I believe it is due to the AMP. How should I go about setting up the new amp? Should I buy the bypass harness in order to fix the tweeters? And is this easy enough to install and wire on my own?

  • Alexander Hrabe from Crutchfield

    Posted on 2/14/2017

    Mike, you will need to bypass the factory amp. An advisor will contact you soon to help you decide on the necessary gear for that installation.

  • KEN from North Las Vegas

    Posted on 2/23/2017

    So will my audio sound better if I get a new stereo to replace the factory one also with new speakers 2 door speakers and 2 6x9s replacing everything factory . The shop told me I have to bypass the amp, just wondering will it sound better or worse . (2001 monte carlo)

  • Alexander Hrabe from Crutchfield

    Posted on 2/24/2017

    Ken, yes, aftermarket gear will step you up from factory sound, but give us a call. An advisor will be able to help you find the right gear for your vehicle to minimize installation headaches.

  • Clayton Hammett from Wellington

    Posted on 3/9/2017

    I bought a jvc kw 925bts from cruthfield. I had it installed today. My factory sub has allways sound really clean. No i can here the words of the song in the sub. Where before the sub only had bass. How can I make it have just the low bass again and get rid of the voice it the sub.

  • Alexander Hrabe from Crutchfield

    Posted on 3/13/2017

    Clayton, you may need to adjust your sub filter to start. Give our Tech Support a call for free help troubleshooting your system.

  • Brett from Streator

    Posted on 4/26/2017

    I have a 2005.5 (new body) jetta. I installed 2 speakers in the back door as well as 2 mid ranges in the front door. For some reason, only my left woofer works and not the right. The headunit I installed was a song mex-xb100bt, which has a built in amp. Should I bypass my amp? And/or, should I put in a old sub+amp that I used in my last car?

  • Alexander Hrabe from Crutchfield

    Posted on 4/27/2017

    Brett, if you're set on keeping the Sony receiver, you'd want to bypass the amp, but with another receiver (without built-in amplification), we have wiring harnesses that would allow you to retain the factory amp. Keep in mind that if you bought your gear from Crutchfield, you can call Tech Support for free help troubleshooting your system. If you purchased your equipment elsewhere, you can still get expert Crutchfield Tech Support - 90 days-worth for only $30. Check out our tech support page for details.

  • Chris

    Posted on 6/18/2017

    I have a 1998 Land Cruiser without the premium sound package (so there's only one connector to the radio), and I connected my AVH-X391BHS through a Metra 70-8112 wiring harness, which what was suggested for my vehicle. I connected all of the wires and RCA cables to the head unit, but no sound. I didn't have the blue/white System Remote Control connected, but when I did, a loud roar would come through the speakers. Should I have not connected the system remote control wire?

  • Alexander Hrabe from Crutchfield

    Posted on 6/19/2017

    Chris, give our Tech Support a call for free help troubleshooting your system. You'll find the contact info on your emailed order confirmation.

  • Jeremy Mayle from Nashville, TN

    Posted on 7/19/2017

    Alexander, Great article here. I'm glad I found it. I was beginning to lose hope in my 2006 Toyota Sequoia JBL amp bypass options. My intent is to replace the factory head unit with an aftermarket version, and replace the door speakers. If I understand things correctly, I'll need to bypass the factory JBL amp and either (a) run the door speakers off of the head unit, or (b) install an aftermarket amp to power those door speakers. Regardless, the factory amp bypass sounds like it's imperative. I was recently told by Crutchfield that there was no specific bypass kit for sale. I'm not opposed to doing it manually, but would obviously prefer the easiest, most economical way. Is that something you could help me with? Many thanks.

  • Alexander Hrabe from Crutchfield

    Posted on 7/21/2017

    Jeremy, unless you have other plans, we'd suggest using a harness that will actually retain your factory amp and allow you to install a new stereo and speakers. I've passed your info along to our Advisors, and someone will contact you soon to help.

  • Kevin Carrera from Miami

    Posted on 7/23/2017

    I have a 07 Acura TL, I bought a pioneer AVH-X5800BHS Double din radio and have it installed already, the shop that installed my radio bypassed my Factory amp. I lost my factory sub (which dont care for going aftermarket anyways) and I had lost my center speaker. My question here is there a way to get my center channel back? Like maybe splicing wires and connecting them together to another wire?? My other question is, by bypassing my factory amp is my aftermarket stereo giving my speakers all the power and frequencies ranges? or is it my factory amp giving it its frequency ranges and the aftermarket stereo just powering up the speakers?

  • Alexander Hrabe from Crutchfield

    Posted on 7/26/2017

    Kevin, I've passed your question along to our sales team to help you find a solution. Likely, you could bridge a 2-channel amp to power that center channel (but you'd want to add another amp to power your other speakers as well), but all told, that speaker might not add noticeably to your overall sound, and therefore not be worth the effort. To answer your other question -- by bypassing your factory amp, you've taken it entirely out of the picture and your new stereo is now powering those speakers

  • Lee from miami

    Posted on 7/28/2017

    I have a 2007 lincoln navigator with THX system without navigation. I want to an aftermarket radio that is double din, sirius xm radio, backup camera option, bluetooth, and hdmi...what do you recommend? also do you have a dash kit for this and wiring harness to keep THX amplified system? I do not need steering wheel controls retrained. please help...

  • Dylan from Rome, NY.

    Posted on 8/11/2017

    Have a 2002 Mercedes Benz ML320. Purchased a pioneer stereo to replace the factory one so I could listen to my music off of my phone, as the factory stereo did not have an option for that. After the installation was done, the guy handed me my amplifier. Speakers sound awful now. Almost no bass at all. My vehicle came with a nice sounding BOSE system. Is there anyway I can have an aftermarket amplifier installed? Would that help?

  • Alexander Hrabe from Crutchfield

    Posted on 8/11/2017

    Dylan, I've passed your info along to an advisor who will contact you soon to help you assess the best steps forward.

  • James W from Pittsburgh

    Posted on 8/25/2017

    Can these bypass harnesses be purchased outright? I'd like to utilize these to wire an external five channel amp in my 2013 Nissan Frontier Crew Cab with "Fosgate" system. I'd like to extract the low level factory amp inputs (factory head unit outputs) and route them to my new amp, then return the new amp's outputs back into the oem speaker wires (factory amp output). Planning this project has been challenging.

  • Alexander Hrabe from Crutchfield

    Posted on 8/31/2017

    James, I've passed your question along to one of our Advisors who will contact you soon to help you find the right gear for your project.

  • Kerby Antoine from East Stroudsburg

    Posted on 9/20/2017

    I have a 2010 Ford Taurus with a Sony Sound System. I want add a subwoofer with a built in amplifier to be my car. The car already comes with a factory amplifier. Should I bypass the factory amplifier and just connect the subwoofer with to the factory stereo while using a Line Out Converter?

  • Alexander Hrabe from Crutchfield

    Posted on 9/20/2017

    Kerby, a powered sub will likely need a speaker-level signal, so you'll actually want to keep the factory amp in the mix and tap into the full-range signal provided to the rear speakers. If you have a factory sub, avoid using the signal supplied to that sub as it will likely be filtered.

  • Brian N Weckerly from Chandler

    Posted on 9/24/2017

    I own a 2015 Chrysler 300 C. Thanks to Crutchfield I was able to bypass my factory amp but I had to keep the factory head unit because it controls everything in my car and no one at this time makes a head unit to replace it. I used the Kenwood Excelon XR600-6DSP and the iDatalink Maestro AR Amplifier Replacement Module. I installed 4 JL Audio C2-690tx in the doors and back deck and Infinity Reference REF-3022cfx 3.5 speakers in the dash. Bass is handled by a Pioneer 10 inch sub powered by a Rockford Fosgate R500X1D amp. My new system was worth every dollar. I can now hear every sound the musicians put in the song. Even the lost kick drums and snare drum that were completely lost in the stock system. All Factory systems are horrible. Replace it as soon as you can if you love music.

  • Alexander Hrabe from Crutchfield

    Posted on 9/25/2017

    Awesome, Brian! Thanks for sharing.

  • Johnny

    Posted on 2/7/2018

    Dose crutchfield have the wire diagram for my factory bose amp-Acura 3.2 cl type-s w/ navigation. I bought a new stereo and speakers from this company

  • Robert shumate from Manila Ar

    Posted on 2/16/2018

    I own a 2001 jeep with infinity. I am replacing the whole system I have installed aftermarket head unit took out the factory amp and replaced all factory speakers and in the process of running New wire for door speakers. Om my amps are getting power my woofers are getting some base but where do I connect my newly ran speaker wires to for sound in the door speakers? I have the factory wiring codes for the connectors in the dash one grey connector and one black one. Those are the Factory speaker connectors. Do I connect my new speaker wires to the factory code wires in the dash for my door speakers? And since I have taken the factory amp out that shouldn't be a factor now as far as sound through my aftermarket head unit right? Or I have my CD player wired incorrectly? By the way I cut the 2 connectors off at the factory amp when I removed it. Just do you know. Thanks

  • Alexander Hrabe from Crutchfield

    Posted on 2/19/2018

    Johnny and Robert, give our Tech Support a call. If you bought your gear from Crutchfield, you can call us for free help troubleshooting your system. Check out our tech support page for details.

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