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Installing a car stereo in a vehicle with a factory amp

Should you bypass the stock amplifier or use it?

Factory amplifier — bypass it or keep it? That's the question we'll explore in this article. Hint: if you want the best sound from your new stereo or speakers, the extra work it takes to bypass the factory amp is totally worthwhile. 

The factory stereo systems in many of today's vehicles include external amplifier. This factory amp 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. 

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

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

In many cases, we'll have wiring solutions for a vehicle that either work with the factory amp or let you bypass the amp. 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 on to 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 wouldn'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. 

How to bypass the factory amp

To bypass factory amp, Dave simply unplugged the cable from the amp and plugged it into the bypass 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.

Last updated 9/18/2018
  • Dave Gubbiotti from Wilkes Barre

    Posted on 7/15/2018

    Which bypass plug did you use to plug into the factory amp. There no link to which bypass pug you used for the 2010 highlander

    Alexander Hrabe from Crutchfield on 7/17/2018
    Dave, give us a call or use our vehicle selector to confirm which harness you'll need with the aftermarket stereo you select. Qualifying the trim level of your Highlander will be an important step.
  • Alexander Hrabe from Crutchfield

    Posted on 5/29/2018

    Bryson, 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.

  • Alexander Hrabe from Crutchfield

    Posted on 5/29/2018

    Anthony, the line output converter will come before the amp. Check out this article for more information and a diagram.

  • Anthony Walker from Rochester

    Posted on 5/28/2018

    Do I put line converter before or after factory amp

  • Bryson from Quartzsite

    Posted on 5/25/2018

    2001 Concorde factory sound was great but I wanted a aftermarket radio and subwoofer install went great aftemarket amp, subwoofers, and radio work fine but I lost my factory amp so I have only subs working now what do I do?

  • Alexander Hrabe from Crutchfield

    Posted on 5/3/2018

    Jeramiah, loose wiring could possibly be an issue. It'll be worth checking all of your connections again. If the problem persists, give our Tech Support team a call. 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.

  • Jeramiah Weller from Edwardsville

    Posted on 5/3/2018

    I just instaled pioneer head unit DEH-P6100BT, a 2 Chan, lightning audio amp b4.250.2 , single subwoofer (Dual's SBX100 10") in my 94 suburban i followed the instal instruction with the head unit and sub box, all worked fine for few mins i shut off the truck latter today while driving i lost my audio, the head unit still had power, jist no sound coming from the speakers the sub still had bass. I thought it was the headunit its self therfore i swapped it out for a Pioneer 3300ub and replaced all the speakers with boss audio brand still same resaults after few mins i lose audio. The truck has an acdelco factory amp under the seat could that be cause of audio loss..?

  • Alexander Hrabe from Crutchfield

    Posted on 4/9/2018

    Adam, from your description, it sounds like you're using a sub output on the Alpine head unit, which should work. Is it possible that there's an option in the head unit menu that allows you to turn the sub out on or off? That could be the problem. Or if the sub level is all the way down. Just be sure to turn the gain all the way down before you try those fixes because you'll suddenly have a lot of bass. If there is no preamp output on the receiver, you'll need a line output converter. Also, 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.

  • adam w. from san jose

    Posted on 4/2/2018

    1996 Mercedes benz c280.... non fiber optic. Cheap alpine aftermarket hu powering the stock amp through the harness. kept stock speakers. Now I added subs and mono amp..... mono amp turns on but no subs pushing. i hooked up hundreds of systems with mono subs no problem. Now learning about bose. So tell me if I am wrong I need to tap in the rear speakers preamp signal via a speaker wire to rca adapter and plug that into the mono amp instead of running rcas from the HU to the mono amp which is what i normally do. Is this because i have the hu signal wires connected via stock speakers via stock amp? im not worried about the hi lo in my situation right? Or am I. I am just as confused as when I had to learn dvc, svc, inline parallel, 4 ohms, 2ohms, running at 1 ohm. Volts,watts,amps.... Whew and all this is just to play some good tunes while your in the car.

  • Alexander Hrabe from Crutchfield

    Posted on 3/5/2018

    Chris, I've passed your question along to our team of advisors. Someone will contact you soon to help you find the right gear for your system. You'll definitely want to install an aftermarket amp to drive that aftermarket sub, and our free Tech Support will be able to assist you with any questions you have.

  • Chris M from San Antonio

    Posted on 3/1/2018

    I have a 2003 Toyota Solara with the JBL system, except the previous owner replaced all of the speakers, including the subwoofer, but not the HU or amplifier. I have ordered a new JVC KD-X350BTS, but I haven't ordered speakers yet as I'm still researching. I have, however, torn the car completely apart to pull out all the old stuff. The Infinity speakers they put in the door were smashed in there, which explains why they didn't sound good. The subwoofer was replaced with what looks like a JBL GTO804 and they used a thick piece of wood behind it to fit it in the factory box. It looks good, but as it is now, what little (very little) bass it produces is muffled by the seat. From what I've read it's not a good idea to use the factory amp, but I would still like to take advantage of the existing subwoofer. How do I go about connecting it to the system when I bypass the factory amp, and would it be beneficial to install an aftermarket amp for the sub? Do you have any recommendations?

  • 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.

  • 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

  • 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

  • Alexander Hrabe from Crutchfield

    Posted on 9/25/2017

    Awesome, Brian! Thanks for sharing.

  • 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 9/20/2017

    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.

  • 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 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.

  • 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 8/11/2017

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

  • 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?

  • 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...

  • 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

  • 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 7/21/2017

    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.

  • 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 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.

  • 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 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.

  • 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 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.

  • 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 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.

  • 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 2/14/2017

    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.

  • 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?

  • 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.

  • 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?


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