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Adding an amp to a premium factory system

How to add power and retain all the features

If your vehicle's factory stereo has cool features but sounds bad, replacing the speakers and adding an amplifier are the best ways to improve the sound quality. Speakers are easy. Amplifiers are more difficult.

In this article, we present three different scenarios describing how to add an amplifier to a vehicle that has a factory amplifier:

  1. Bypassing the factory amp in a full-range analog system.
  2. Using an aftermarket amp with signal-summing inputs for a crossed-over factory system.
  3. Using a vehicle-specific interface device and harness for a digitally controlled system.

We'll explain what all of this means as we go.

Upgrading your vehicle's premium stereo system

The factory stereo system in your car does everything you could possibly want it to do — except sound good. Replacing the speakers and adding an amplifier is the best way to upgrade sound quality, even for so-called premium systems. Replacing speakers is a fairly straight-forward operation, covered in our How to install speakers guide. We also show how you can add a subwoofer to a factory stereo, if that's all you want.

When upgrading the power of an amplified factory system, however, technical issues often arise that complicate the installation of an aftermarket amplifier — like factory stereos with digitally controlled amps that power different speakers with different signals in different situations.

JL Audio VX800/8i

JL Audio VX800/8i eight-channel amp with digital signal processing

Keeping the features you like

For example: many cars feature Bluetooth® communication and warning chimes playing out of a center channel speaker while lowering the volume or muting the other speakers. In order to retain those features, the new amplifier must duplicate whatever the factory amp was doing. 

One way to do this is to use the factory amp's processed, mixed, and powered outputs for your aftermarket system's inputs. Another method utilizes the factory system's digital software controls to incorporate your new amp into the system, so it'll do just what the factory amp did, only better.

And in some cases, the factory amp may have to remain in position, and a signal-summing amp connection or a digitally controlled interface device may be required for a successful aftermarket amplifier installation.

In the sections below, we'll discuss what's going on in each scenario and how to work with it. If it gets confusing, don't worry. You can always call us and our Crutchfield Advisors will let you know what you'll need for your vehicle.

Scenario 1 — If you're lucky, the factory system is all analog

In rare situations, you may be able to simply replace your vehicle's factory amp with a new one. If there are no digital connections between the radio and the amp, and the amp's full-range analog input signals respond to the radio's volume control, you can remove or bypass the factory amp and replace it with your own aftermarket amp.

AudioControl D-6.1200

The AudioControl D-6.1200 six-channel amp with assignable high-level inputs is a great choice for a factory system upgrade.

How can I tell if it's an analog system?

Typically, you'll only find such all-analog factory amps when there are only four channels in the whole system. (Counting a factory component set consisting of a tweeter and a woofer as one speaker.) The amp will have four pairs of wires (eight total) going to its inputs, and the same for its outputs.

You can tell for sure by probing each wire pair (usually a colored wire plus the same-color wire with a stripe) using a signal generator and sensor with a speaker or a real-time analyzer (RTA) to identify each source signal and each speaker. Unfortunately, most people don't have access to that kind of test gear, so listening carefully will be the best tool to use.

How do I replace the factory amplifier?

After removing the factory amp, you can use its input wires, which carry the analog output signals from the factory radio, for your aftermarket amplifier's inputs. Then, you can connect the factory amp's output wires to your new amp's outputs. This will send the signal (music) on to the speakers through the factory vehicle wiring.

You can do this by cutting the plugs off of the factory amp harnesses and connecting the wires to your amp, or you may find a vehicle-specific amplifier bypass harness that'll do the job without any wire-cutting. If you do cut plugs, you may want to save them, with useful lengths of wire attached, so you can return the system to stock if you choose to un-install your amp upgrade

Line output converter

This installation-in-progress photo shows an Audio Control LC7i line output converter using two load-generating devices on its high-level inputs.

What do I need to do it?

Your aftermarket amplifier must have speaker-level inputs capable of handling the radio's output level, or you'll need line output converters (LOCs) to level-match the amp's inputs to the radio's outputs. Another issue is that without its normal output connections, the factory radio may shut down or show an error code. If this is the case, you'll need a load-generating device on each speaker channel.

Most of the time, our Advisors can let you know in advance if these items are needed, so give us a call before you get your new amplifier. After you get an amp, our Tech Support team can help with any issues. Learn more in our article about using line output converters and load generating devices in a factory system.

Wavtech link6

Wavtech link6 six-channel line output converter.

Scenario 2 — When there are highs, mids, and lows on separate channels

This scenario is pretty common these days. Whether your factory amp has all-analog or digitally controlled inputs, you can use its powered output signals for your aftermarket amp's inputs. This way, each channel of your new amp will play whatever the old amp channel was playing.

A common problem with this method, however, is that the output from the factory amp consists of processed, crossed-over signals. Each channel has a different high-, mid-, or low-frequency range of signals. For example: your tweeters will play high-frequency notes like cymbals, the mid-range door speakers will play vocals, guitars, and keyboards best, the rear speakers may play the full range of sound, while the subwoofer channel plays only low-frequency bass notes.

The solution: Signal summing and matrix mixing

A great way to handle this situation is to combine the signals of the different factory channels to form one full-range signal. Then you can process and amplify that signal any way you want, to make it sound best to you. To do that, you'll need to use an amplifier or digital signal processor that features high-level inputs and the ability to re-route and mix input and output signals.

161D61200 close up

AudioControl's D6.1200 amp can combine high-frequency, midrange, full-range, and subwoofer speaker-level inputs to form a unified signal to amplify.

What do I need to do it?

Some devices, like Wavtech line output converters, allow you to combine, mix, and balance input signals automatically or by using a wired remote control. Other devices, like JL Audio digital processors and VXi Series amplifiers and AudioControl D Series amps and processors, use software control apps to mix and assign signals as well as control the overall sound quality. The interactive graphical user interface controls for these devices are often beautiful, comprehensive, and complicated.

JL Audio Tun in a ford

JL Audio's TüN processor graphical interface showing assignments, EQ, and more

What to do when that doesn't work right

In some vehicles, after summing and amplifying the signals from the factory amp, you may find your speakers playing with weird frequency responses and equalization curves meant to protect cheap factory speakers. Also, your vehicle's warning chimes and voice prompts may be too loud or too soft, or some other audio functions like automatic noise control (ANC) and bass roll-off just don't behave or sound right.

In these cases, you'll need an interface device that understands all the vehicle's digital commands and translates them for your aftermarket amp to obey and play correctly.

Scenario 3 — Vehicle-specific all-features solutions

The best way to add a new amplifier to your car is to use a vehicle-specific interface device and harness designed for adding amplification to a factory system. This will allow you to integrate into the factory stereo and get clean, full-range, and flat (unequalized) input signals for your aftermarket amp, that will work and sound like they're supposed to.

What do I need to do it?

Products that will help you add an amp include:

PAC AmpPRO AP4-FD21

PAC AmpPro AP4 aftermarket interface module and harness for select 2012-up Ford vehicles

These devices work with vehicle-specific harnesses, usually sold separately, that let you install your amp upgrade with minimal or no wire-cutting or splicing required. Some interface modules require firmware updating and flashing via an internet connection to the manufacturer's website.

How do I install these devices?

The interface module connects behind the factory radio, so it'll receive, translate, and send along all the factory system's signal and control information to your aftermarket amp. Then you connect a bypass harness to the factory amp's output harness, so you can send your aftermarket amp's outputs to the speakers through the factory speaker wiring.

Depending on the vehicle, you'll either access all the speaker wires in one location at the factory amp's output connection plug or connect to them individually throughout the vehicle wherever the factory wires run, like behind kick panels and door trim. The vehicle-specific bypass harnesses usually take this into account.

iDatalink HRN-AR-FO2

This iDatalink HRN-AR harness connects a Maestro AR amplifier replacement module to select 2011-up Ford vehicles

What you should do

If you know how to use audio test equipment, like a multimeter or an RTA, then you should have no trouble figuring out what you need for your amp installation. On Crutchfield's website you'll find amplifiers, vehicle-specific amplifiers, sound processors for factory radios, and the factory system upgrade cables necessary for the job.

Tech support

Crutchfield Technical Support Specialist Jeffrey — ready to help.

For everyone else, contact us to get the right gear. Crutchfield Advisors have access to a vast database of vehicle information that includes what kind of factory system is in your vehicle, what aftermarket speakers and amplifier will fit, and what interface device, if any, will work best to produce the best-sounding aftermarket system for you and your car. Plus, when you buy your gear from Crutchfield, you get access to our legendary free tech support to help you build and enjoy your perfect sound system.

Last updated 2/22/2022
  • D's Notes from Wichita

    Posted on 4/23/2022

    What are the products? And what kind of GM do you have? I have a GMC Yukon xL SLT 2004 and I'm having trouble finding a y harnesses that integrate my OnStar, SWC, and factory amp bypass... It's crazy.

    Commenter image

    Buck Pomerantz from Crutchfield

    on 4/25/2022

    D, It appears that there's presently no pre-made T-harnesses available for your vehicle. To add an amp, you'll have to use the factory amplifiers' outputs for your aftermarket amp's high-level inputs. Make sure it can handle at least 12V, otherwise you'll need to use a line output converter (LOC) for the amp's input.
  • Salami Samuelson from to many to list

    Posted on 3/30/2022

    For several modern Chevrolet models, [I found a couple products that work. I] didn't have to splice any factory speaker wires, add any pre-amps, or run signal cables or even a remote/antenna switch cable. I maintained full functionality of the factory system including the Bose noise cancelation without adding any obnoxious overcorrection. Just clip the wiring harness together and run a power cable. The amp has a smartphone tuner app that was easy to use. Perhaps the easiest sub/amp installation I've ever done (but not the least expensive or flexible). There may be similar wiring harnesses for non GMC vehicles.

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