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Lead image

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 an 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 Crutchfield CSW9W-20 9-wire speaker cable, 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 to help via phone or chat.

Dave in his car

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

  • Zackary Lawton from Venice

    Posted on 6/9/2022

    So I have a 2003 Toyota Camry with a factory amp and a JBL sound system me on my speaker freak and the car already has a 8 job speaker system but I want to keep that and add an additional four more aftermarket speakers and subwoofers in the trunk so do I need to bypass the factory Amp and connect all the stock speakers to a new amp and the aftermarket speakers to another amp or could I keep the factory amp and somehow run RCA's off it to the other Amp powering the aftermarkets and then run an RCA from that amp to the subwoofer amp

  • Cecile Adams from Berkeley Springs

    Posted on 5/22/2022

    So why can't you just leave the factory amp RCA plugs unplugged in the aftermarket stereo

  • Scott from Vancouver

    Posted on 2/25/2022

    The factory speakers are 2ohm, so by just replacing the factory speakers and listening to it with the factory amp still attached it was only doing half the power of the original setup. Just something to think about

  • Jared from Montclair

    Posted on 2/19/2022

    I think the decision should be about the big picture. If the 2002 Highlander has the same stereo design as a 2003 4Runner (JBL system), one would find a loss of the center dash speaker if bypassing which would kill the JBL sound choices. However, there are not many direct speaker replacements due to the mix of Ohm ratings across the 10 speakers. My point is to investigate and evaluate your options based on your budget, your time, and your overall A/V expectations.

  • Ashley Green from Crittenden

    Posted on 2/7/2022

    I have a 2004 Hyundai sonata. I want to put an aftermarkwt stereo in and also add an amp and subs. Can I just run all new speaker wire from my inside speakers to my amp like I normally would if there wasnt a factory amp?

  • Willie Darden from Detroit

    Posted on 10/14/2021

    Ok Crutchfield, let me put you to the test or challenge. What can you do with a 2017 Cadillac XTS with the CUE system outfitted with the premium Bose speaker system and a sub mounted in the back deck? The system seems to kill the bass as you turn it up (I guess to prevent speaker damage) and it also looses some frequencies like it's muffled sometimes. Can you even upgrade that system? What size is the sub (can't find any info on it) and what is it's rated power? (Can't find that info either) If you have any answers feel free to contact me.

  • Kermit

    Posted on 8/21/2021

    Using a 20 year old vehicle bears little relationship to the electronics in modern cars. It would have been more useful to compare using a car made within the last couple years

  • Eric Baumgartner from Kyle, TX

    Posted on 7/9/2021

    I'm 'bout to pull the trigger on the 2019 RAM 2500 mega cab. Keeping the 8" UCONNECT "stereo" but dumping the active noise cancelation tech and the factory amp & speakers. I want to purchase a package that'll draw out more highs and deeper lows. The current stereo sounds like they stuffed socks in where the tweeters are. And the low end is attenuated as you turn up the volume to save the RAM crappy speakers. I hate that!!!!

  • Kevin Segers from Herentals

    Posted on 6/13/2021

    I need some help. I bought for my mazda cx-3 of 2017 new component speakers for in the front and coaxial for the rear. My car has an factory amp, now my question is should I place a new amp for the best results and how do I have to do it, what amp would I need?

  • James camacho from Tucson

    Posted on 4/7/2021

    I need help on how to understand and how to this to my car. I don't want to take apart my whole dash to hook up everything that way. I would much rather bypass my cars stock amp wiring since it's located in my trunk. I want to install a 2 amps one for my sub and one for my main inside speakers. The only thing I currently have is a 8 guage power cable running to the back which was hooked up to a old amp and i was tapping into the stock sub in the back to give me the signal for my subs which that converter went bad. I'm going to run a new 4 guage all the way to the back. I already have a fuze box in the front but will need a 3 splitter fuse box in the back to power 2 amps and maybe something else later maybe a cap or something not sure but currently stuck on where to get my signals from. And how to do it. I drive a 2013 kia optima axl I've already found the stock amp located behind the right side trunk panel and i have access to the harness that's connected to the stock amp but i dont know what I'm suppose to do from there in order to get signal for new amps. I'm also looking for a 2 channel amp for the subs and 4 channel for the inside speakers but still those are stock for the mean time i will probably install a pair of kicker speakers for the front doors. But i really would like to know how can I go about hooking ip this system with out accessing the stock stereo.

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