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How to Bypass Factory Amp Step By Step

Many of today’s vehicles come equipped with a factory amplifier. The latter is designed to make factory speakers sound better. Most often, this won’t do you any favors when you replace the stereo or those stock speakers. So, at some point, you’ll just have to bypass it.

It goes without saying that if you want the best sound from your new headunit or speakers, the extra effort and time it takes to bypass the factory amp is totally worthwhile.

What is a factory amp bypass?

Basically, a factory amplifier bypass is removing your factory amplifier or more specifically its functionality from your system.

Technically speaking, by bypassing the amplifier, you’re sending the audio signal (non-amplified) directly from your radio straight to the speakers. Remember, the amplifier sits between your stereo and your speakers.

Why would you need to bypass your amplifier?

There are many reasons why you may need to bypass a factory amplifier, the most common of which is when the factory amplifier is not producing enough quality, going bad or just not working anymore.

Looking for better sound quality – which entails upgrading the factory stereo and the speakers – is another reason why you’d need to bypass your factory amp.

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

First and foremost, it must be noted that not all car audio problems can be solved with a factory amplifier bypass. After all, not all vehicles come with a build in factory amplifier to bypass in the first place.

Furthermore, not all car stereo systems are built the same, so bypassing or keeping the stock amplifier depends greatly on your setup, and your plans.

Retaining the factory amp

Most often retaining the factory amplifier makes it easier to install a new aftermarket stereo, and in some vehicles that’s your only option. But in such case, your new stereo’s sound is limited to what that amp can do.

Bypassing the factory amp

Bypassing the amp takes time and effort because you have to run the bypass harness to the factory amp, which is often located in some other part of the car, such as under the passenger seat, in the trunk, under the rear seats …etc.

The extra work, however, is worth it because you’ll get better sound from your new stereo, even if you’re keeping those factory speakers.

This sounds counterintuitive, right? Doesn’t an amplifier mean more power to the speakers which results in better sound ?

Well, it’s not just about the power. Most factory amplifiers also include some sort of a filter or crossover network for specific frequencies that may not sound optimal with a new system. So, bypassing the amp makes total sense when you’ve replaced the factory speakers with aftermarket ones.

How to bypass factory amp without harness

First of all, it should be noted that in most cases, it’s easy to bypass the factory amplifier. Other times, it’s a nightmare without the right adapter.

I mean, some typical car audio systems are pretty basic, and have a simple amplifier that’s driving the front and rear speakers. On the other hand, some of the more premium systems go further and feature an extra channel for the subwoofer.

The thing here is that if your vehicle comes equipped with a fancy audio system featuring a subwoofer, and you decide to bypass the amplifier without using the right harness (which can costs upwards of $100), the receiver will only drive the four speakers, but not the subwoofer.

Furthermore, some premium amplified systems come equipped with radios and amplifiers that retain the door chimes, seat belt warnings and some other safety features, which you definitely don’t want to lose by any means when you bypass the factory amp without harness.

These extra features and warnings can make the task of bypassing the amp even more tedious and time consuming to the point where you’re better off purchasing the right adapter or harness.

We get it. The price tag on those amp bypass harnesses is a tough pill to swallow, and most often people don’t want to pay the extra dollars, and just want to do the bypass without it.

All in all, bypassing the amp without a harness won’t matter much if you have a basic setup consisting only of a pair speakers, or in case you have plans for your audio system down the road (replacing the speakers, adding an aftermarket sub & amp …etc). However, if you’re just replacing the headunit, I’m afraid you could be missing out on some features and some channels that you wouldn’t be able to power with your aftermarket headunit. In a case like that, it’s highly recommended to buy the adapter.

So, to do a factory amp bypass without a harness, follow the steps listed below:

1- Locate the amplifier

First of all, you need to locate your factory amplifier. As we’ve mentioned above, a factory amp location depends on your vehicle. Some cars have it somewhere in the trunk, some have it under the passenger seat or under rear seat, some have it in the side kick panel, some have it in some sort of nook and cranny inside the dashboard …etc.

If you couldn’t figure out where the amp is located, google is your friend. It has all the answers to most of your problems. We can’t count how many times it helped us with such things.

2- Remove the headunit

Though each car is unique and different in complexity, removing the radio itself is actually a pretty easy job for the most part. But to get to that point, you’ll first have to remove the dash trim pieces. For that, you need some trim removal tools (including nylon prying tool). The latter will help you remove the radio without damaging the dash panel.

Once the trim pieces are out the way, proceed to removing the retaining bolts (if there are any). Next, try disconnecting the electrical connectors and the antenna from the back of the radio. Then pull it out.

3- Check the wires (harnesses)

Now, that you’ve located the amplifier, pull the harnesses out. One of those plugs goes to the receiver, but which one? It’s hard to tell without testing. To figure out which one, you’ll need to use a multimeter and test for continuity between the radio’s harness and the harness you just unpegged from the amplifier.

The multimeter tests continuity by sending a little current through one probe, and checking whether the other probe receives it.

So, what you want to do basically is to put the black probe on the multimeter in the factory radio’s plug, and put the red probe in the other side of the amp to see if any of the colors match.

4- Find amp’s power and ground wires

The amp’s power wires are usually the fatter wires or sometimes matching pairs.

To find which of those wires are your amp’s power wires, switch your digital multimeter to “DC” (direct current), and put the negative probe to a solid “ground” on the vehicle such as a bolt or any unpainted metal surface.

Next, use your positive probe to probe the wires on the harness. When your meter reads around 12v or so, you have found your power wire.(write the color down).

Now, keep that probe on the power wire and use the black probe to check the other wires on that harness. When your meter reads around 12v, you’ve found the factory ground wire. (write the color down)

5- Identify input wires

After you have identified your power wires and wrote them down its time to find your input wires.

Your input wires are the wires between your stereo and you’re amp. They take the audio signal from the headunit to the amplifier.

Your output wires are the wires between the amp and the speakers. Their main role is take the amplified audio signal from the amp to the speakers.

To figure out the input wires, you need to do a continuity test between the harness you unplugged from your headunit and the harness on the other side of the amp.

Try to find the wires at the stereo harness that match the wires at the amplifier. If you find a matching set of wires make sure to test them with your multimeter set to “continuity”.

In case you don’t see any matching wires, you’ll need to do a bit more work.

To find input wires when there’s no matching pair, you’ll need to put one of your probes on one of the smaller gauge wires on the radio harness, and start to probe the wires that were attached to the amp one by one. When you find a match you’ll here a “beep” tone. You found it! Note it.

Now that you’ve found your input harness its time to move on to the the other plug.

If your amp has only one plug then both your input and output wires should be on this harness. If it has multiple plugs, you will need to move to the other harness.

6- Verify speaker wires

To verify the speakers wires (output wires) at your amplifier harness, you’ll need to unmount your speakers and keep note of the speaker wire colors for each speaker and the location of the wires.

With your speakers removed, run a continuity test with your multimeter from your amplifier harness to confirm which wires are which (which ones go to the front left door, which ones go to the right rear door …etc).

Before returning the speakers back into their mounting location, you need to do a phase check on each speaker to see which of its wires is the positive and which is the negative (aka testing for phase).

Continuity test all your speakers and write down all the wire codes. Once that’s done, you are all set to criss-cross the two harnesses off.

7- Criss-cross the wires

Now that you’ve have figured out all the wires (input, output, power and ground), and you’ve written them down you can cut the harness and make the connections at the amplifier location.

  • Cut the wires at the plug(s) all at once. It’s recommended to leave at least 4 inches of wire on the plug.
  • Make sure to cap off or tape the ends of the power and ground wires at the plug to avoid any shorting to your radio.
  • Strip about half an inch from each wire to make a connection.
  • Using the butt connectors, start to make your connections and crimp wires one by one.
  • Once all the wires are joined together, mount the headunit back into its location and test the fader and balance on the deck.
  • If everything works fine, you’re done! Congratulation. You’ve successfully accomplished bypassing the factory amp without harness.

Alex Brown

Hey There, my name is Alex Brown, I'm an LA-based sound engineer with over 10 years experience installing, troubleshooting, and repairing commercial, automotive, and household sound equipment. I've installed highly competitive car audio systems, and everything from navigation systems to full car stereo systems, remote starters, alarms and beyond. I enjoy creating solutions and simplifying everyday needs. I also love helping people get great sounding gear, thereby, saving the world from bad sound one customer at a time.

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