How To Hook Up A 4 Channel Amp To Front And Rear Speakers

Adding a 4 channel amp is a great idea. I’ve enjoyed powerful, crystal-clear sound in my vehicles for years using my own 4 channel amps.

But how do you hook them up?

In this guide I’ll show you how to hook up a 4 channel amp to front and rear speakers. After installing hundreds of amps in vehicles just like yours I’ll share with you the fundamental tips you need for great results.

And hey – don’t worry…in most cases you can do it yourself and get professional results on a budget!

Infographic – How to hook up a 4 channel amp (tips and general guide)

Hook up amp 4 channel amp front rear speakers infographic diagram

Basics first

If you’re reading this there’s a good chance you’re not familiar with installing an amp, connecting wiring, and other details related to hooking up a 4 channel amp in a vehicle.

Not everyone has installed car stereo equipment before so I’m going to be as thorough as possible and avoid making any assumptions about how much you know.

What is a 4 channel amp?

Holding Alpine MRV-F300 amp in my hand

Today’s 4 channel amps offer newer technology, better sound, and more compact size than in the old days. An excellent example is the Alpine MRV-F300 50W x 4 model. It uses class D amplifier technology to run extremely cool and yet it’s small enough to fit under a car or truck seat. Very nice!

What a 4 channel car amplifier is may seem obvious at first but there’s a bit more to know Additionally, there are some interesting (and good) ways they differ from 2-channel amps.

In fact, there are actually a few benefits you’ll get using one 4 channel amp instead of 2 stereo ones to power your front and rear speakers.

A 4 channel amplifier is a stereo amplifier with 2 more channels built in to boost (amplify) weak input signals to a higher voltage signal. This drives speaker voice coils to move the speaker cone and produce sound.

4 channel amplifiers add more channels into a more compact and efficient design than separate amplifiers would have.

Additionally, they offer more flexibility, as most can be configured for “bridged” operation which can give more power when you don’t need all 4 channels.

What is “bridging” an amp?

Bridged mode capability is a special design feature in which a “push-pull” set up is created: one channel (normally used for the left speaker) produces a signal that’s the opposite of the second channel (normally used for the right speaker).

This causes the speaker to receive a voltage audio waveform that is the difference between the two channels – resulting in more available power to speakers.

Essentially, bridged mode is a flexible way to get more power if you’re not driving 4 speakers. It means 2 channels are sharing the workload of one speaker between them and therefore and drive it with more power. That’s helpful if you’d like to hook up 4 speakers and a sub to one amp.

2 channel vs 4 channel amp diagram

2 channel vs 4 channel amp diagram

A 4 channel car amp is basically an expanded version of a 2-channel amp. However, because they’re built together and not 2 separate 2-channel amps, they’re more compact. This saves installation space and makes it easier too. Additionally, most can be bridged to use 2 channels (or 3, depending on your needs) so you’re not restricted to using them with only 4 speakers.

The benefits of using an amp to drive speakers

Whether you have a factory stereo or a great aftermarket (non-factory) one, adding an amplifier is one of the best decisions you can make.

In-dash stereos are very limited in how much power they can produce. They can’t drive speakers with the same clarity and low distortion as a good amplifier can.

The maximum volume you’ll be able to get from your speakers will be pretty low, too.

There’s simply no way around it – most in-dash stereos are limited to about 15W-18W RMS of power for each speaker channel. That’s because they’re running directly from the +12V supply. Amplifiers are unique in that they take the +12V electrical supply and boost it to a higher voltage.

When a signal is boosted and sent out to your car’s speakers the voltage is much higher and the speaker can receive much more power.

That’s why tiny amplifiers are rarely worth bothering with – if there’s no special power supply inside, it’s simply not capable of producing much power.

Getting great sound

Powering speakers from an amp makes a big difference, and I’ve enjoyed excellent sound for years this way.

When an amplifier drives your vehicle’s speakers it’s often not even pushed to its limits. The sound produced at the speaker has lower distortion, doesn’t “bottom out” when heavy bass is played, and you can get a lot more volume, too!

Additionally, using an amplifier with built-in high-pass crossovers means you can block out lower-end bass that causes your speakers to distort and attempt to play music tones they’re not suited for.

The result is cleaner sound, less distortion, and great volume – you can crank your music even higher!

Just imagine driving down the road with the windows open and finally being able to blast the music you love. I’m confident you’ll love it as much as I do.

Things to know before you start

Clip art image of a face thinking - Things to know content image

It only takes a few minutes to make a list of the parts, wire, tools, and other bits and pieces you’ll need. Planning ahead can mean the difference between getting your system going without major problems or having a frustrating time – or complete failure! I always get organized and get my items together before I start a job.

Planning ahead is very important. You don’t want to run out of wire or discover you don’t have the rights parts, for example. That will mean you can’t finish your project.

It’s even worse when you have to drive around town searching for items or you’re not able to do anything after the stores close. Believe me, I’ve been there, and it’s terrible!

Notes about wire, tools, and a few other things

When it comes to installations, always plan to have more, rather than not enough, wire. This goes for speaker wire as well as RCA cables.

The amplifier kits I recommend have the right length for your amp installation, but speaker wire & RCA cables are another matter in this case.

What length and size speaker wire do I need?

wire of 16 ga speaker wire

There’s no need to spend an excessive amount of money on speaker wire. 18 gauge is enough for many installations, but 16 gauge is a great choice too if the price is right. A great example is this AmazonBasics 100 foot roll. I recommend a 100 foot roll for many installations with a 4 channel amp (see why below).

Here’s an estimate of the worst-case scenario for the length of speaker wire required. I’ll use the example of installing an amp using speaker-level inputs, with the following typical installation:

  • Amp is located in the trunk
  • Speaker level signal connections near the radio (center console)

Let’s use roughly a 15′ length of distance from the radio to the amp. That’s a good estimate in my experience.

So we have:

  • Wire from the radio to amp (signal wire): 4 channels x 15′ = 60 feet
  • Wire from the amp to speaker wiring near radio: 4 channels x 15′ = 60 feet

Total estimated wire required: 120 feet.

That means you need 2 100 ft rolls of wire. Or at the least, 1 100 ft roll and 1 50 ft roll. If you’re planning to use a line-level adapter, expect to pick up a 100′ roll.

If your installation is using RCA jacks, expect a 100 ft roll also (4 channels x 15′ length estimate for the speaker wire from the amp).

What about RCA cables?

KNU Conceptz KCA-K4 4 gauge amp wiring kit RCA cables imageIf you’re installing a 4 channel amplifier and using RCA cable connections, you’ll need to buy a 2nd pair along with your amp wiring kit, as most only include a 2-channel cable.

For most installations, I recommend 18′ length cables. That’s usually long enough for most vehicles and you should usually have enough length to hide the cables inside the interior and under the rear seat, etc.

There’s no reason to spend an excessive amount of money. Just pick up some good quality, well-made cables. Even No products found. will be fine in most cases.

Tools you’ll need.

Image showing example crimp tool and crimp connectorsCrimp tools are great for installing your amp and speaker wiring with professional results. If you’re doing your own installation, you can get by with an inexpensive tool like this Pros'Kit crimp tool. Crimp connectors are sold separately in many automotive parts stores or general stores and are very affordable.

I recommend a few tools. If you shop carefully, you can avoid getting ripped off on tool prices. When connecting speaker wiring to factory wiring, it’s easier to use crimp connectors than solder.

Never simply twist the wire together and wrap it in electrical tape. Always use a reliable connection.

During warm weather, electrical tape adhesive can fail and the tape can come off of the wire. This exposes it to possible short circuits and potential damage to your radio or amp.

If you have access to a cordless drill, that’s fantastic! They’re great for drilling holes in the vehicle’s metal for mounting your amplifier or connecting the ground wire to bare metal.

I also recommend the following:

  • Wire cutters (some crimp tools have this built-in)
  • Roll of quality electrical tape
  • Wire ties (“zip ties”), 6″ length, bag of 100
  • A digital test meter for voltage measurement

Etekcity MSR-R500 digital test meter example

A test meter is often incredibly helpful when installing an amplifier. However, you don’t need to spend much money! A basic but good budget model like this one at Amazon will work great.

I recommend getting an affordable but good digital test meter to find a switched +12V wire for getting a remote-on signal to the amp.

They’re also extremely helpful when troubleshooting power problems when something isn’t working.

Get your installation shopping list together

Image of a paper checklist being prepared with a marker

Here’s a general but pretty accurate list of what you’ll need for connecting a 4 channel amp to front and rear speakers.

Installation types 1 or 2: Factory radio or no RCA connections

  1. 4 channel amplifier with speaker level inputs or amp and line-level adapter
  2. 120 feet or more speaker wire, 18 gauge or larger
  3. Amp wiring kit
  4. Crimp tool and butt (wire crimp) connectors (25 or more at least)
  5. Cutting pliers
  6. Electrical tape
  7. Wire ties, 6″, bag of 100
  8. Test meter

Installation type 3: RCA connections

  1. 4 channel amplifier with speaker level inputs or amp and line-level adapter
  2. 100 feet roll speaker wire, 18 gauge or larger
  3. Amp wiring kit
  4. Additional RCA cables, 18′ minimum
  5. Crimp tool and butt (wire crimp) connectors (25 or more at least)
  6. Cutting pliers
  7. Electrical tape
  8. Wire ties, 6″, bag of 100
  9. Test meter

Be sure to plan well and estimate the amount of speaker wire you’ll need. For the amp installation itself, I strongly recommend using a pre-made amp wiring kit like you’ll find here in my amp kit buyer’s guide.

You’ll also need to get a 2nd pair of RCA cables. I recommend 18 ft length or more. Don’t spend too much money, but do get decent quality ones.

How to get a signal to your amp

Example of the rear of a car stereo installation closeup

Image of an aftermarket (non-factory) stereo showing the RCA jacks and speaker output wiring. Either one can be used for getting a signal to an amp, but RCA jacks offer a better option. They’re normally lower distortion and allow using plug-in RCA cables. If those aren’t available, either an amp with speaker-level inputs or a line level (speaker level) adapter can be used.

In order to install a 4 channel amp and drive all 4 speakers, in many cases, the biggest obstacle is getting a signal to the amp. Once that’s done, the rest is usually a standard amp installation.

There are 3 basic ways to get a signal to your 4 channel amplifier:

  1. Connect speaker outputs to your amp’s speaker level inputs
  2. Connect a line-level adapter to the radio then use RCA cables to the amp
  3. Connect your radio to the amp using RCA cables directly
NOTE: I won’t be covering factory sound systems that are “premium” and have a factory amplifier. Those such as Bose, JBL, and Mark Levinson, often found in luxury vehicles or special-edition models, are much more complex and harder to deal with.

In that case, my advice is to speak with a good installation shop first and do your research.

If you feel that factory amplified systems should be here as well, send me a message or comment and let me know

In a few cases, adapters are available to connect an amp to a factory amplified system’s audio wiring, but it’s often difficult or there are obstacles you won’t find until you get started.

One of the reasons why is that factory amplified systems often have non-standard wiring connections for the audio path and are prone to bad noise problems if you connect an amplifier without the proper adapter or wiring.

Which type of connection do I need?

If you have a radio with RCA jacks, skip on down to the next section.

However, if you have a stereo with no RCA jacks (which is always the case for factory-installed stereos) you’ll have to buy one of the following:

  • A “line level” converter
  • An amplifier with speaker-level (“high level”) inputs

1. Line level converters

PAC LP7-4 4 channel line level converter

Line-level converters like this PAC LP7-4 4-channel model are designed to take speaker-outputs from a stereo with no RCA jacks and adapt them to RCA jacks. Using this, you can run RCA cables to your amplifier.

Line level converters are designed to allow connecting to an amplifier’s RCA inputs by converting speaker outputs from a stereo to a low-level signal an amp can use.

It’s very important to buy a quality, well-designed line-level adapter to avoid noise, poor sound quality, and other problems. Don’t get the cheapest – instead, get a name brand model you can rely on (like the one above).

2. Speaker level inputs

Car amplifier speaker level input example
Amplifiers with high-level (speaker-level) inputs like this one allow connecting to speaker wiring for a signal source. This avoids having to buy a separate adapter.

Speaker level inputs are common on many 4 channel amplifiers. These amps contain electronics that scale down speaker wiring signals to a lower signal safe for the amplifier’s input circuitry.

They’re simple to connect: normally it’s just a matter of connecting both positive (+) and negative (-) wiring for each speaker channel on a small wiring harness included. This then plugs into the speaker level input connector.

4 channel amp speaker level harness example

A typical speaker-level input harness for a 4 channel amp. The wires are color-coded to make installation easier. White = left front, gray = right front, green = left rear, and purple = right rear.

While it can save money (you won’t need a line-level adapter in this case) I often recommend that people consider buying a line-level converter anyway.

This allows an easier upgrade for your stereo later, which is very common for people to do. Using the line-level converter now will allow you to run RCA cables to your 4 channel amp to be used later if you buy a better stereo (which will include RCA jacks, almost always).

3. RCA jack (line-level) connections

RCA jacks offer a clean, lower-noise connection than speaker-level adapters do, but honestly, it’s not noticeable to the average person. RCA cables (line-level connections) are the preferred way to connect a signal to your amp if you have that option.

RCA jacks on the rear of a Pioneer head unit. This is the ideal way to connect your amplifier’s signal inputs, if available. For a 4 channel amplifier, you’ll need 2 stereo RCA cables to do so. White represents the left channel white red represents the right. These are standard colors for audio outputs for both car and home stereo.

If your stereo has RCA jacks, then congratulations. Things just got a bit easier – and potentially better sounding, too!

You’ll need 2 stereo RCA male-to-male cables (4 audio channels total) to run from the radio to your 4 channel amp. That’s 4 signal channels: left & right front and left & right rear.

4 channel amp signal connection diagram

Here’s a helpful diagram showing the most common connections you’ll need to make one of the 3 most common cases I mentioned earlier:

  1. Connecting to your amp’s speaker level inputs
  2. Using a line-level converter
  3. Connecting your amp to the radio’s RCA jacks

4 channel amp signal connection diagram
You can also click here to view the .pdf document for print or download.

Connecting and running signal wiring

Speaker-level connections

As mentioned above and as shown in the diagrams, if you’re using speaker-level outputs to get a signal from the radio, you’ll need to connect wire. Ideally, you’ll do so near close to the radio, then run the wire together as a bundle.

You can bundle speaker wire together with wire ties to keep it neat and make the installation easier.

Estimate the length of speaker wire you need to reach the amp (or line level converter) for each audio channel. To do so, run a length of wire from the radio to where the amp will be installed, then allow a little extra and enough length to run around curves and interior parts.

Cut 7 more lengths of wire, for a total of 8:

  • 4 channels (4 pairs of wire) going to the amp’s speaker level inputs
  • 4 channels from the amp to the radio’s factory speaker wiring

Image of car stereo wires crimped

I recommend connecting to speaker-level outputs using crimp connectors and a crimp tool for a reliable, solid connection. Blue connectors are normally the right size for 18-16 gauge wire.

Factory stereo color codes

If you have a factory stereo, you’ll need to find the wiring colors for the speaker wiring.

A great resource for that is, where you’ll find wiring diagrams for your vehicle and color codes listed.

Making connections

Image of factory stereo wiring harness

After removing the radio you’ll find connectors like this for the factory stereo wiring harness. You’ll need to separate the speaker wires, cut them, and attach wiring to run to the amp.

Remove the radio and disconnect the factory wiring plugs or aftermarket radio’s wiring harness.

Cut the speaker wires, leaving enough length to move the wire and to have enough length to connect to the wire freely.

Strip a small part on both the stereo’s speaker wire and your amp speaker wiring. If using a line-level adapter, connect to the stereo’s speaker output side. Then connect the 4 pairs of wire to the speaker wiring in the harness.

Insert the stripped wire (about 1/4″ of bare wire) into the connectors and crimp them carefully using a crimp tool if you have one. Alternately, you can twist together wire, solder it, and carefully wrap it with electrical tape or use heat shrink tubing for insulation.

If using speaker level inputs on your amp, also connect 4 pairs of wire to the output of the stereo.

Wire bundle with zip ties example

To make a neater, more professional installation, bundle the speaker wiring similar to this using wire (“zip”) ties. I recommend using 6″ ties which often are sold in packs of 100.

Once all wiring is connected, bundle it up using wire ties or, optionally, a little bit of electrical tape wrapped around. In both cases spacing out wire ties or tape about every 1″ or 1.5″ along the length of the wire works well.

Connecting RCA cables

Example of connecting RCA cables to rear of a car stereo

Connecting RCA cables to an aftermarket (non-original) stereo for running to an amplifier.

If you’re using a line-level converter or have a stereo with RCA jacks, connect all 4 cables plugs to the front and rear outputs.

RCA cables are sometimes marked with left and right symbols (“L” and “R”). In some cases, white, clear, or some lighter color can be used to represent the left channel.

Connect the cables consistently so you’ll be able to recognize which one is which. If the front and rear RCA cables are the same, you might want to mark front and rear using some masking tape and a marker or pen.

Connect the remote-on amp wire

Don’t forget the remote wire! Amp wiring kits include a small wire that’s used to connect the amp so that it switches on and off with the accessory position of the ignition switch.

Locate a +12V wire that has power when the ignition is switched to “ACC” or similar but turns off with the key. You may also have good luck finding an existing wire color from vehicle wiring diagrams I mentioned earlier or from a Google search.

I recommend checking the wiring even if you have already located it online, just to be sure.

Before re-installing the radio connect this wire and run it alongside the speaker wiring.

How to connect a 2 ch. car stereo to a 4 channel amp

Diagram showing a 2 channel car stereo connected to a 4 channel amp

You can connect a head unit car stereo with only 2 channels (left and right) to a 4 channel amp easily. Ordinarily, all you need is 2 RCA Y adapter cables. The head unit’s left channel RCA jack should be connected to the left front and left rear amp inputs. Likewise for the right channel. If using speaker level inputs on the amp, use the connections shown above. NOTE: Use only ONE of the two connections above! Never connect both types at the same time! Speaker-level outputs will damage RCA connections.

If your head unit (car stereo) only has 2 RCA jacks or two pairs of speaker outputs, that’s not a problem.

As shown in the above diagram, you can connect 2 channels to a 4 channel amp using either the speaker level inputs wired in parallel or by using simple RCA adapter cables.

RCA y adapter cable image

All you need is a decent pair (a total of 2) female to male RCA “Y” adapters No products found.

The sound quality will be exactly the same. Today’s amps are designed in such a way that there’s no harm in using a Y adapter to connect the amp. The amplifier will receive exactly the same signal, with the same quality, in the front channels as well as the rear.

The only drawback is there won’t be a front to rear fader control like with head units with 4 channels of outputs.

After connecting the stereo to the amp, you’ll need to adjust the rear gain to set the volume level for the rear speakers as needed for the proper volume depending on the stereo’s signal strength.

Installing the amp

Product image of Belva BAK82 amp wiring kitAn amp wiring kit like this one will make installing your 4 channel amp much easier. A good-quality one like this Belva 8-gauge complete kit includes not just wiring but much more. You’ll also need to pick up a 2nd pair of RCA cables (if using them) and enough speaker wire.

Your amplifier needs a good solid metal connection to ground and you’ll need to run the positive battery wire to the engine compartment. Your amp wiring kit will also include a fuse holder that should be installed near the battery as well (most kits include instructions, by the way).

You’ll also need to connect the amp’s speaker outputs to the wire you ran from the radio. Here’s a basic diagram as well to help:

How to install a 4 channel amp diagram

Setting up your amp

Alpine MRV-F300 4 channel amp end viewOnce installed, you should set up your amp’s gain levels and crossovers for the best sound. In this image, you can see the adjustable crossovers for both front and rear channels. Turn on the high-pass crossovers and adjust to a setting close to 50-60Hz, to allow good bass for music but block low-end bass that distorts.

Once installed, you’ll need to set up your amp’s gain levels and crossovers, if available. Most sold today have that. (See my recommendations at the end for some great models)

Gain control is the amount of signal amplification the amplifier performs. Ideally, with a good input signal, it can be kept low to reduce any hiss or noise that can appear when it’s turned up high.

Here’s a great rule of thumb for how to adjust the gain for this type of system:

  1. Turn down gain controls on the amp
  2. Turn the stereo’s volume to 2/3 of maximum
  3. Slowly raise the gain controls until the volume is enough

When finished you should have enough volume available from the stereo but noise should be minimal. You’ll still need to tweak it a bit if the volume is too high or too low.

Setting the crossover

As I mentioned at the beginning of this guide, using high-pass crossovers will allow more volume with less distortion and will help protect the speakers from heavy bass.

For both front and rear channels turn on the high-pass feature and, if an adjustable dial is available, set it near 50 to 60Hz. Some models don’t offer an adjustable frequency for the cutoff but are likely preset to a good level.

Test and tweak

Once installed, test and tweak your amplifier as needed. A great way to mount your 4 channel amp is by using a board mounted to the car, covered with speaker box carpet or other material.

Play some music you’re very familiar with and adjust things like bass, treble, and the fader as needed. Using music you’re very familiar with (of high quality) means you’ll be able to notice any problems with the sound fairly easily.

If you don’t already have one, you might consider later upgrading to a head unit with built-in equalizer (EQ) functions to help tailor the sound.


About the author

Marty is an experienced electrical, electronics, and embedded firmware design engineer passionate about audio and DIY. He worked professionally as an MECP-certified mobile installer for years before moving into the engineering field. Read more »

Your comments are welcome.
  1. I have the NVX 400 4 channel amplifier. It says I can bridge 4 ohm car door speakers with the lowest impedance at 4 ohms. Do I need to add a power Inline resistor or do I wire front speakers in series then parallel to amplifier? I’m confused. Any help will be greatly appreciated. I only want to bridge the 2 front speakers. All speakers are 4 ohms. BTW, I love this site, have learned so much.

    • Hi Jerry & I’m happy to hear you found my site helpful.

      Unfortunately in this case, bridging the amp won’t acheive anything helpful. If you bridge the amp and wire the front & rear speakers in parallel and add a series resistor to get the total Ohms load back to 4Ω, 1/2 of the power will be lost across the resistor(s) as heat. That would defect the purpose. You’ll also lose the front & rear fader ability.

      If you really need more power on the front speakers, you can bridge it and add a 2nd amp to power the rear ones. Less power should be ok for those. However, the NVX amp has pretty decent power so unless you really need the extra power, I’d leave it in 4 channel operation.

      Hopefully that helps!

  2. I’m confused on the entire input and outputs.
    My amp had a input for front and output and input for rear . My head unit has front and rear and then a sub ..Can you explain the best way to have installed

    • Happy Thursday, Susan! The subwoofer output(s) on your head unit is a “nice to have” option, so it’s completely optional. What you use depends greatly on what speakers you’re powering with the amp.

      For full-range speakers, you’d use the front/rear RCA outputs. For subwoofers, you can use either the sub RCA outputs or the rear. The difference being that the subwoofer outputs typically offer more options or convenience since you can make adjustments from the head unit.

      That’s as opposed to using the built-in low pass crossover/bass boost/etc. on the amplifier.

  3. Thank you so much for sharing this detailed information. It saved me a hundreds or a couple of thousands if I will have it set up with the professional.

    Just a quick question about using the line output converter.

    1. Can I connect a 2 channel LOC to the front speakers then just use an RCA y to connect to a 4 channel amplifier?

    2. My goal is not to access the factory radio since it is a lot of work to do plus I am replacing all the 4 factory speakers anyway.

    3. If I will wire separately the fours speakers goin to the amplifier, do I need to disconnect the factory connected wires from the speakers or shall I just tap?

    Thanks in advance.

    • Hi Rodel.

      1. Yes, you sure can.
      2. Understood.
      3. You can just tap off of them, when using most line output converters. That’s because most (aside from a few like the PAC SNI-35 with a lower input resistance) have a high input resistance. This the radio will still “see” a normal Ohms load at its outputs.

      In case you want to learn more I have some more info in a recent article I wrote about LOCs:

      Have a good day.

  4. Hello,

    I am replacing a cd/bluetooth single din in my boat, and the 6.5 speakers. I was wondering if I could get some help and possibly talk to someone ? The current set up has one channel on a 4 channel amp being used for the sub, and a remote wire to the deck, and 4 6.5’s powered by the deck. While I am not very good at this, the system works, but it sounds like I might be able to make it better.

    Dave 714-402-7536

    • Hi David if you like you can contact me directly. See my Contact page via the top menu for 2 ways to reach out.

      If you can, please specify:
      – The amplifier brand & model number
      – The subwoofer type & impedance (Ohms)
      – The head unit model

      Long story short, most likely the amplifier doesn’t have enough power with only 1 channel to power the subwoofer. May amps can be bridged to get 2x the power and drive a subwoofer if it’s at least 4 Ohms.

      Best regards.

  5. Rodel,
    Let me explain that a little better.
    I think this is a 2 channel amp. Left pos and neg, and Right pos and negative.

    The battery in the boat is next to sub and 2 channel amplifier. One pair of speaker wire from 1 channel (left pos and left neg) on the amp connected to the sub, and 1 red wire “remote” goes over to the deck. I have 4 6.5 speakers im assuming are powered by the deck. The funny thing, I see RCA cables coming from the deck and what looks like go over toward the amp, but the additional wires are not there? So, anyway that is my setup in a nutshell. My 6.5’s were blown when I bought this boat, the deck has an intermittent connection (which is the push button to release the faceplate, just a bad spring that does not keep the connection tight) so I am replacing the 4 6.5’s and the deck….pretty simple since everything is there.

    • Hi, if you’re not sure if the 6.5″ are powered by the deck you can check the speaker outputs on the amplifier. You should only see the subwoofer speaker wiring.

      Regarding that, the amp with have a +12V remote, ground (-), and battery +12V, and RCA(s) connections. If the amp is bridgedable (I can’t say, since I don’t have the model number), then power the subwoofer with it bridged if it’s a 4Ω subwoofer.

      It depends on the specifics of the head unit and amp as far as to what your sound options are (low pass crossover, bass boost, etc.).

  6. Hello again. I finally installed everything however upon connecting the RCA from the 2 channel LOC to the 4-channel amplifier it shuts down. But if I disconnect one of the RCA from the LOC it was fine but still the amplifier is not working. I tapped the LOC to the front left and right speakers. The LOC has only one red extra wire which I do believe is the power and connected it to the amplifier 12v. What do you think is the possible issue? Thank you.

    • Hello, There’s no reason a LOC should cause an amplifier or other things to shut off it it’s connected correctly. I suspect that perhaps you’ve created a short somewhere based on what you wrote. Most LOCs also don’t require a power connection, so I’m not sure what brand/model you’re using.

      You’ll need to provide more specific info about the LOC brand & model number, specifically how it’s connected, wiring between it and the amplifier, etc. in order for me to help you more.

  7. hello i have a kicker mono amp for my two woofers and a sony explode 4 channel amp with 4 Sony 3 way mids speakers and a Sony head unit worked great till i blew the deck now i have a head unit with no sub jack what do i do about the 4 speakers on the 4 channel amp ive got my woofers on the rear on the head unit but on its own amp now i gotta figure out these 4 speakers that go to my 4 channel amp and only front hook up to that how do hook up the 4 speakers ive got two sets of rcas coming out of the amp and i only have room for one set

    • Hi, you can just use a RCA “Y” adapters to send a signal to RCA inputs on both the 4 channel amp and the subwoofer amplifier.

      Best regards.

  8. so the sub woofer is cool it sounds great,,……quick ,,question now about the Y’s the double RCA will go to the amp and the single RCA one goes to the radio QUESTION IS do i have to do anything special with speakers or do i connect then regular to the amp i have 4 speakers its a 4 channel im gonna put the y’s in just making sure i didnt have to double up on speakers or bridge them together or ?

    • Yes, go from the head unit with a pair of RCA cables to the “Y” adapters then out to each amplifier. You don’t have to do anything special with the speakers, if I’m understanding your question correctly.

      Just wire one speaker per channel on the 4 channel amp.

  9. Hey, quick question
    I’m using a Boss Chaos650 4 channel amplifier to run 2 midrange speakers and a subwoofer (dual 2), a power acoustik pwm 20 preamp and a pioneer dh-s1100ub head unit which only has one pair of RCA outputs. How do I wire the system to get efficient midrange and bass output?

    • I think by “midrange” you mean “full range” actually. Strictly midrange would have no, or only greatly reduced high frequencies.

      You don’t really need the equalizer, so skip that and use “Y” adapters to connect the Pioneer to the amplifier. Then use the amp’s built-in high-pass & low-pass crossovers. Have a look here.

      > Also, what settings should I use on the head unit to get a full range frequency output?

      It should be in the owner’s manual. It’s likely already full-range by default. Best regards.

  10. Hello, great write up, thank you! I am going to attempt all this myself and I think I have everything and it all makes sense. I have a Boss double din aftermarket stereo with RCA connections on the back so will be going that route. I recently replaced rear, front, and tweeders with JBL club series, so now I need to have something to power them! I purchased a Recoil DI550 4 channel amp and a Recoil PCK84 8gauge wiring kit. With your diagrams, I think I’m good to go. But I have 2 questions. 1) to be clear, the speaker wires coming from the new amp will be connected to the speaker wires in the rear of the headunit, AFTER I cut them from the harness of the headunit, correct? The whole point is we want to bypass the headunit amp, right? if so, then 2) the speaker wires for the tweeders will still need to connected to the headunit harness, right? The new 4 channel amp has nothing to do with the tweeders so those will still need to be powered by the headunit? Thanks!

    • Hello there Darrick.

      1) Yes, if you’re referring to connecting your new amp to the factory speaker wiring, that’s correct. You would then insulate the speaker output wires from the head unit (you can use good quality tape, crimp connectors, or something else reliable to prevent a short on the speaker leads.)

      2) Technically it would work to power the tweeters with the head unit, but here are several reasons why you don’t want to:
      a. The head unit has far less power and will reach distortion sooner than the amp.
      b. The amp can provide better sound quality, which is especially important with decent quality tweeters.
      c. The tweeters and the speakers powered by the amp will have different power (and volume) levels.

      If your front JBL spekaers are full range, you can add high-pass crossovers to the tweeters and use them in parallel with the front speakers. If the JBL are component type woofers, using 2-way speaker crossovers will work well. Best regards.

      *(Note: I mention adding crossovers to the tweeters if they don’t already have them.)

  11. Alright i need some help.
    I have an aftermarket hu that has 2 rca out (front/rear). I want to run 2 amps…
    Amp 1- full range alpine mrp-f300 which is 4 channels.. im assuming use the 2 rca for inputs. The question here is im using 4- 4 ohm door speaker and also have a 5th dvc speaker for the center. How should i wire this 5th speaker?
    Amp 2-is for sub kicker 300.1. Question here is where do i get the input? Im assuming a loc which i have the lc2i but unsure on how to wire it for sub use. Also would it need to be connected to the speaker wires from the hu or can i tap into the speaker wire after the 4 channel amp? I assume it would have to be pre amp.

    • Hello, Jason.

      1. You can just use RCA “Y” adapters to connect the two RCA outputs to both amplifiers via the rear RCA outputs. It’s ideal not to use a speaker to line level converter if you have access to RCA outputs.
      2. It is possible to connect the 5th speaker if you like but be aware it won’t be a true center channel – it’ll be a mono output (L + R channels combined).

      You can connect the 5th speaker & front speakers in “tri-mode” since the Alpine is a bridgeable amp. To do so:
      – Wire the front speakers one per channel as normal..
      – Add a 4 Ohm power resistor in series with the 5th speaker (creating 8 Ohm total).
      – Connect the speaker to those front channels in bridged mode per the amp’s lablels/instructions.
      – Add a speaker L-pad for 8 Ohm speakers to the 5th speaker. You can mount it wherever is most convenient for you.

      You’ll need to reduce the 5th speaker’s volume via the L-pad. That’s so it won’t override the main front speakers (and hurt sound). You’ll usually want to adjust the output level also for the best sound.

      Both parts are fairly cheap and not hard to find. Best regards.

    • Hi Jason. It won’t work well running a single speaker off of a stereo head unit. Also, if the speaker volume for it will be disproportionate with those connected to the amp.

      My advice would be to wait about connecting the 5th speaker until you have the parts I mentioned earlier (for connecting to the amp), or don’t use it at all.

  12. Question: when wiring 4 speakers to a 4 channel amp; which is channel #1, which is #2, etc
    I’m sure for the balance & fade to work it makes a difference. Also, unclear as to wiring the “remote” power wire.
    Thanks for a great article. I’ve done fog lights & heated seat wiring and just want to know in advance exactly what I’m doing. I have not purchased the amp yet and hoping it might have instructions…..

    • Hi Lloyd. They’re *typically* labeled, although in some odd cases it can be confusing as they may not be.

      It is usually: Ch 1 = Left, Ch 2 = Right, Ch 3 = Rear left, Ch4 = Right rear. For a 4 channel amp, generally there’s not “technically” a front pair/rear pair, but 1/2 are usually used as front and 3/4 as rear.

      Some amps may have a certain feature (like bass boost) only on the 2 rear channels.

      The remote-on lead uses a low current ~12V signal to turn the amplifier on. You can use a very small gauge wire for it (it usually draws less than .05A). I would be surprised if your amp doesn’t have at least basic instructions, so don’t stress over it. :)

      Glad you like my article, and have a good day!

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