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Car amplifier installation guide

Step-by-step instructions for wiring an amp

Q: How do I install an amplifier?

A: Read this article! We cover all of the basics of where to mount and how to wire the amplifier. And we'll walk you step-by-step through the installation process. We'll also share a few expert tips and tricks along the way.

This installation guide offers examples of amplifier installation and layout. Installation specifics will depend on the make and body style of your vehicle and the equipment you purchased.

Before going through this more-detailed guide, you might want to watch our amplifier installation video to get an overview of what's involved:

Preliminary considerations

Before we get into the installation, let's talk about some of the details:

  • What installation accessories do you need?
  • Where should you put the amp?
  • How and what do you dissassemble in order to run wires?

What wiring and accessories do I need?

Car amplifiers don't come with any wiring included. You must supply the amp's power and ground wiring, an inline fuse, a remote turn-on wire, RCA cables, and speaker wires.

007CPWR1 Amplifier power wire

Power and ground wires

The power and ground wires need to be thick enough to accommodate the amp's demand for electrical current or the amp won't operate properly or put out its rated power.

Your amp's instructions will include a recommendation on what size wire to use. Or, you can check out How to determine the best size wire for help doing it yourself. Don't forget to measure all distances first, so you'll know what lengths of wire to get.


The fuse that will protect your system

The in-line fuse on the main power cable, mounted within six inches or so of the battery connection, is essential for protecting the wire, your car, and you from a catastrophic fire in the event of a short circuit. Each wire manufacturer rates their wire's current capacity differently, but as a general rule, for a typical 16- to 20-foot run, you'll be safe using a:

  • 25-amp fuse with 10-gauge wiring
  • 60-amp fuse with 8-gauge wiring
  • 100-amp fuse with 4-gauge wiring
  • 250-amp fuse with 1/0-gauge wiring
007CK4 Crutchfield 4-gauge amplifier wiring kit

An amplifier wiring kit

The easiest way to get these items is with an amplifier wiring kit, which will include matching power, ground, turn-on wires, and fuse.

120RCA174 RCA patch cables

RCA cables and speaker wire

Amp wiring kits often don't include signal wiring. Your amplifier gets its input signals from the receiver's output typically via RCA cables. RCA cables come in stereo pairs, in various lengths.

When running new speaker wires from your amplifier's output to the speakers, any size wire from 18- to 14-gauge will work fine. (The lower the gauge number, the thicker the wire.) For subwoofers, use 16- to 12-gauge wires.

Where should I mount my amp?

Use these guidelines to choose a location for mounting your amplifier. A smart mounting location will help your installation go smoothly:

  • Follow the manufacturer's recommendations for mounting the amplifier and make sure it's secure. An amp that isn't secure could break loose in an accident and injure someone as it flies through the vehicle.
  • The amp should be at least three feet from the stereo to avoid noise radiated from the vehicle's electrical system. The amp can also interfere with the stereo's AM/FM reception.
  • Do not bolt your amplifier directly to your car's metal chassis — that's inviting noise problems, like ground loops which hum or buzz. You could use rubber grommets around the mounting screws to isolate the case. Or you could mount the amp onto a wooden board or plastic panel and attach that to the car body.
  • An amp produces damaging heat during operation, which its heatsink absorbs and radiates away from the circuitry. The amp needs a few inches of air space around it to stay as cool as possible. Never mount an amp upside down, as dissipated heat will radiate back into the amp.
  • Make sure there's enough room for you to connect the wiring and adjust the controls (gain, crossover, bass boost, etc.).
Amplifier mounted in trunk

A compact subwoofer amplifier mounted in an out-of-the-way nook in a trunk with plenty of air space for cooling

Good locations to install an amplifier include:

  • On the firewall (passenger side)
    Pros: You can use short wires and patch cords. You won't have to remove a seat or climb into the trunk.
    Cons: Only very small amps fit here. This puts your amp close to some common noise sources.
  • In the trunk or hatch area
    Pros: Plenty of room for large amps. Near the rear speakers. Easy access to the amp controls.
    Cons: You sacrifice some cargo space. Longer wires and patch cords are required.
  • Under a seat
    Pros: Closer to the receiver, so you can use shorter patch cables and signal cables, which are less prone to noise and signal degradation. Closer to the front speakers, so running wire to them will be easier. No cargo space sacrificed.
    Cons: You may have to remove the seat to do the installation. Warning: removing your seat could deactivate your vehicle's SRS (airbag) system. Only small amps will fit. The amp will need to be protected against water from rain or snow brought in on shoes.
Running wires

Where do I run the wires for my amp?

All system wiring should be concealed for safety, and to give your installation a nice, finished look. Wires should be secured so that they do not interfere with safe vehicle operation. Depending on the location you choose for your amplifier, the wiring may need to be run under the dash, door scuff plate, pillar trimpanel, or kickpanel.


Bojo trim panel tools

The instructions below address, in general, which panels may need to be removed and how they typically come off. Often, panels can be pried up at the edges. You'll probably also need to remove some screws and retaining clips. To prevent damage, always use care when removing panels — a panel tool is helpful.

Removing the door scuff plate

The plates are usually removed by prying up the edges to release clips. Some vehicles will have screws present which will need to be removed.

Scuff plate

Removing the seat belt

A seat belt may be located on a panel that needs to be removed. Most seat belt anchor covers pry off. The seat belt anchor is secured with a large nut or bolt.

Seatbelt cover

Removing the pillar trimpanel

Remove the seat belt if present. Remove screw covers, screws, and plastic retaining clips if present. Pry up the edges of the panel to remove it.

Figure 4-5

Removing the kickpanel

Look for screws and pry-out retaining clips to remove. Pry out the edges of the panel to release and remove it.


Routing wire behind the dash

When routing wire behind or under the dash, always secure it with plastic wire ties. Be sure that the wire doesn't interfere with any moving parts to ensure safe operation of the vehicle.

System diagram

Time to install the amplifier

With that background stuff covered, it's time to get to work. Gather up your gear and tools, maybe a friend and a soda, and give yourself plenty of time.

Step 1 — Disconnect the battery

Set the parking brake and disconnect the negative terminal from your battery to prevent any electrical shorts or shocks.

Step 2 — Mount the amplifier

Mount your amplifier in the location you've chosen.

Step 3 — Install the power wire

The power wire from your amp wiring kit (usually 16-20 feet in length) needs to run from the battery, through your car's firewall, through the car's body to the amp. Find an unused grommet in the firewall or one that already has wires or cables passing through it and that has enough room for the power wire to fit through too.

Running power wire through the firewall

Route the power wire from your amp wiring kit through a hole in your vehicle's firewall, using a grommet or bushing to prevent the insulation from scraping against metal.

If you can't find an existing grommet, you'll have to drill a hole through the firewall. Make sure you don't drill into any electrical or gas lines — check both sides of the firewall. Use a grommet to protect your wire from fraying and shorting as it passes through the hole.

Fuse near battery

Fuse installed on power wire, and secured in engine compartment near the battery.

Step 4 — Install the fuse holder

The power wire from your amp wiring kit may have a fuse holder installed. If so, go to Step 5. If not, find a good spot close to your battery to place your fuse-holder (included in the kit) — less than 6" from the battery is best. Be aware: even after a fuse blows, the short stretch of cable between the battery and the fuse holder will still be live and a potential fire hazard in the event of an accident. Anchor the fuse holder to a suitable spot with a screw or cable tie, so it won't hang loose or bounce around.

Fuse holder

Cut a short piece off the end of the power wire (to cover the distance from the battery to the fuse holder location), and strip the insulation off both ends with a wire stripper. Crimp the terminal ring (included in the kit) onto one end of the short piece of wire, and attach the fuse holder onto the other end. Strip the insulation off the end of the power wire that leads into the passenger compartment, and connect it to the other end of the fuse holder.

Multi-amp installations

When powering multiple amplifiers, you run a single heavy-gauge power cable from your battery to a distribution block, and then connect a lighter-gauge cable from the block to each amplifier. This arrangement minimizes potential noise problems and keeps your installation looking neat. Make sure the main power cable is thick enough that it can handle the total current draw of all the amplifiers.

Check out our amplifier wiring diagram to see how the wiring gets connected in a typical 2-amp system.

Step 5 — Connect the power wire

Attach the power cable to the positive battery terminal (not directly to the battery post itself). For top-mounted battery posts, the most common way to do this is to crimp a ring terminal onto the end of the power cable (many cables in wiring kits come with it already attached). Remove the battery terminal's nut, slip the power cable's ring over the bolt that secures the battery terminal to the battery post, and replace the nut. For GM vehicles with a side-mount post, we offer terminal adapters that work nicely.

A wire loom provides added protection for your wire against the high heat inside the engine compartment. If your kit includes a wire loom, thread it over the power cable until it reaches the firewall and cut to fit. Thread another piece over the short power wire running from the fuse holder to the battery.

Step 6 — Ground wire: the most important connection of all

As near to the amplifier's location as possible, find a bolt to your vehicle's metal frame to use for ground. If you can't find a convenient ground screw or bolt, drill a hole for one — be careful not to drill into any wiring, the gas tank, or a gas or brake line. Crimp a ring terminal (usually included with the amp kit) to the short piece of ground cable (also in the kit).

Ground wireScrape away any paint and clean the bolt location thoroughly, and then bolt the terminal tightly to the vehicle's metal chassis so the ground connection will be bare metal to bare metal. Use a lock washer, a star washer, extra screws, and any other technique or device that'll keep this connection tight, clean, and electrically conducting. Many people even coat the final connection with silicone caulk to prevent corrosion.

Improper or loose grounding is the #1 cause of amplifier problems.

Step 7 — Install the remote turn-on wire

The turn-on wire (also called the remote wire) is located behind the stereo. On aftermarket stereos, it's usually a blue and white wire. The remote wire will "tell" your amplifier to turn on whenever the stereo is powered up (usually, whenever the vehicle is turned on). You'll have to remove the stereo to get to this wire. For step-by-step instructions on removing your vehicle's radio, see your vehicle-specific Crutchfield MasterSheet™, or read our Car stereo installation guide.

Remote turn-on wire

Locate the remote turn-on lead behind your radio (usually a blue and white wire), and connect the turn-on lead from your amplifier wiring kit to it.

Strip the insulation off a small section of this wire coming from the radio and the turn-on lead that came with your wiring kit and connect them together via solder, a crimp connector, or a Posi-Connector.

The turn-on signal is +12 volts DC. If, like a factory radio, your radio doesn't have a remote turn-on output, then you can get the turn-on signal from your vehicle's fuse box. Because of its low current demand, you can connect your turn-on lead to almost any fused output terminal, like the one for the radio itself for instance, as long as it only powers up when the vehicle's on. Using an Add A Fuse connector plus a 2A to 10A fuse will make this connection easier.

You'll need to route the turn-on lead to your amplifier through the car's body — it's often easiest to route the turn-on wire with the RCA cables (next step) but you can also route it with the power wire after it passes through the firewall. The power and RCA cables should run on opposite sides of the vehicle, to reduce noise — but it won't matter for the turn-on lead's low current.

Step 8 — Making the signal connections

If your in-dash receiver has preamp (RCA) outputs, connect your RCA patch cables to them. Route the patch cables to the opposite side of the vehicle from the power cable. It's important to separate the patch cables from the power wires as much as possible to avoid potential noise problems. Now you can partially re-install the radio in the dash. Avoid completely re-installing it if you can, in case you need to fix a problem later.

If you're using a factory radio with no RCA outputs, you can get your amplifier's input signals from the factory speaker wiring. The speakers will be getting their signal from the new amplifier — which leaves the radio's outputs available to use for the amp's inputs. There are two ways to do this: get a line output converter (LOC) that'll adjust the speaker-level signal for your amp's input, or get an amplifier with speaker-level inputs. You cut the factory speaker wires behind the radio, and connect the wires coming from the radio to your LOC or amp's inputs.


Scosche SLC4 Line Output Converter

Learn more about line output converters.

Step 9 — Speaker wiring

Now you have to provide a way for the music to get from your new amp to the speakers. The best way to do that is to run a new speaker wire from each amplifier output to each speaker. Use 14- or 16-gauge wire for speakers, 12- or 14-gauge for subwoofers. Speaker-level signals are not very prone to picking up interference, so it's okay to run your speaker wires near power cables.

Amp wire under back seat

Running wires is all about finding the best path. Here, we're running a bundle of speaker wires across the backseat to the amp in the trunk.

You'll have to run each wire for your door speakers through the rubber gasket or boot around the hinge, to protect the wires from the weather or from getting pinched in the door. There may be a Molex plug or a similar obstruction blocking the way, but you can usually find a place to drill a hole through it big enough to fit your wire through. Disconnect or cut the factory speaker wires and connect the new wires directly to each speaker terminal.

It is important that you keep the polarity of your speaker wiring straight. This means that each positive terminal of the amp connects to a positive terminal of a speaker — and the same goes for the negative terminals. This ensures that your speakers will operate in mechanical phase — all the speaker cones moving the same direction with the same kind of signal — and will sound balanced when playing together. The positive and negative terminals of each speaker should be labeled, but if not, the positive terminal will usually be wider than the negative terminal.

Use your factory speaker wiring

Another and much more convenient way to send the powered signal from the amp to your speakers is to run the speaker wires to the harness that’s behind your receiver, where all your car’s speaker connections are accessible in one place. You cut each speaker wire from the receiver's harness and reconnect it to a speaker wire coming from the amp. Then, the signal can flow from the amp to the speakers by way of the vehicle's original factory wiring. This technique will work fine in systems with up to 75 watts RMS of power per channel — but for more powerful systems it would be better to run new speaker wire directly from the amp to each speaker.

Check out How to connect an amplifier to a factory stereo to see how this can be done.

Step 10 — Connect all the wires

Neatly drape or trim each wire and connect it to the amp. Make gentle curves with the wires, not sharp bends that could pinch. Many people cut small slits in their vehicle's carpeting and run their wires underneath, for stealthy installations that look factory-neat. A wiring snake comes in handy for this. Tape your wires to the snake, fish it under and through to where you want your wires to go, and pull them on through.

RCA cables plugged in

RCA cables routed through slits in the vehicle's carpet, and connected to the amplifier's signal inputs

Step 11 — Turning it on

Check all of your wiring, from the battery and receiver to the amp and speakers, making sure every connection is tight and secure with no stray wire strands laying out that could cause a short circuit. Especially, check that the ground connection is tight and secure. Set all the amplifier's gains to minimum, and turn off all the filters and any bass boost or EQ it may have. See that the main fuse is properly installed in its holder. Then, reconnect your car's negative battery cable.

Turn on your car, then turn on the radio. Verify that the amplifier powered up (there'll probably be an indicator light on it somewhere). Play some music and turn the volume up just loud enough to hear. Now verify that sound is coming from each speaker and/or subwoofer in your system. If everything sounds right, you can finish re-installing the stereo and all your vehicle's paneling, and then move ahead to step 12.

Step 12 — Setting the amp's gain

Setting your amplifier's gain, or input sensitivity, matches the amp's input level with the receiver's output level, resulting in maximum distortion-free music and minimum background noise.

Gain setting on an amplifier

Setting the amp's gain

For a detailed explanation of how to do this, read our article about setting the gains on a 4-channel amplifier. If you’re installing an amp for a subwoofer, read How to tune your subs. The approach is the same, we’ve just tailored the explanation to each situation.

Enjoy your new system.

Ivy adjusting gain

When things go wrong 

Usually, once you've installed your amp, you can turn on the stereo and immediately enjoy all the extra power and detail in your music. But sometimes things just don't work like we expect them to right from the start. If this happens to you, don't get stressed out too much. Read our article about troubleshooting your amp installation for help with finding and solving the most common problems.  

Lex installing amp

Give us a call — we'll help you outfit your system

Your best first step is to call Crutchfield and talk to an Advisor about what your amplifier will need. They'll make sure you get all the necessary hardware and accessories for a successful and satisfying installation. And remember, anything you buy from Crutchfield comes with free lifetime tech support. Just click on "Contact Us" at the top of this page for the toll-free number and other methods of contacting us.

  • Reggie in Mile High from Denver

    Posted on 9/15/2021

    My current set up is using a factory installed Rockford Fosgate 10 speaker system in a Nissan Titan with an aftermarket HU. I'm wanting to put in a 4 X 100 amp and upgrade the lower door speakers. Is it okay to continue to use the factory Fosgate amp for the 3 dash and upper door speakers while using the RCA outputs from the HU to send signal to the amp for the 4 lower door speakers?

    Commenter image

    Buck Pomerantz from Crutchfield

    on 9/15/2021

    Reggie, You can do that only after you disconnect the lower door speakers from the factory amp, so each speaker won't have two amp outputs connected to it, trying to blow each other up. You can connect your new amp's outputs to the factory speaker wiring, to avoid having to run new speaker wires throughout your car.
  • Merea from Muncie

    Posted on 9/10/2021

    Someone gave me a Jensen 420 2-channel amp to put with my 2 Kenwood Kfc-w3013ps subs and I don't think the amp will push the 2 subs. The amp can do 110 W x 2 @ 2 ohms but my subs are 400 W RMS SVC 4 ohm each. Could I use the Jensen or should I just stick to my 300 W x 1 @ 4 ohm bridged Rockford Fosgate P3002?

    Commenter image

    Buck Pomerantz from Crutchfield

    on 9/11/2021

    Merea, One of those amps can power two of those subs with 65 watts RMS each and the other can power them with 75 watts RMS each - which is less than 20% of their power ratings. They deserve a more powerful amp. Using both amps each bridged to power a sub might be your best option using the gear at hand to power one sub with 170 watts RMS and the other with 200 watts. Otherwise, I recommend getting a mono, 1-channel subwoofer amplifier that can put out up to 800 watts RMS at 2 ohms.
  • Beto

    Posted on 8/3/2021

    Suggested edit. No need to display this. Fairly common knowledge, but still... Specify which terminal on the battery to connect the power cable to.

    Commenter image

    Buck Pomerantz from Crutchfield

    on 8/3/2021

    Beto, There's no need for such an edit. In step 5 we state: "Attach the power cable to the positive battery terminal ..."
  • tim w simons from Abingdon

    Posted on 7/13/2021

    So I installed a jvs assassin 1200 watt amp to run 6x9. Problem is only bass no highs. What is wrong.

    Commenter image

    Buck Pomerantz from Crutchfield

    on 7/14/2021

    Tim, An online search for the amp you name comes up with zero suggestions. It does, however, sound like you have a mono subwoofer amplifier with a low-pass filter engaged. This is an inappropriate amp for a full-range speaker.
  • doug from parrish

    Posted on 7/5/2021

    I will be replacing a stock head unit of a Ford f150 with a Kenwood head unit. Truck has an after market Alpine amp installed years ago. What needs to be done to use your ready made wire harness and SWC that I have ordered from Crutchfield along with the Kenwood ?

    Commenter image

    Buck Pomerantz from Crutchfield

    on 7/6/2021

    Doug, If you purchased your gear from Crutchfield, you're entitled to free lifetime tech support. Give us a call so someone can fix you up.
  • Dave from Atlanta, GA

    Posted on 6/29/2021

    I am installing an older 45 watt per channel (80 max) two-channel amp in the back of my 48-year-old car and running an 8-gauge wire for it. My question is: do I need also need an 8-gauge fuse holder (at the battery connection)? I have one, but it is huge. And since the amplifier only requires a 20-amp fuse, it looks like overkill. A 10 or 12-gauge fuse holder would fit in the space near the battery better. But (always a but!) I don't want to choke down the 8-gauge wire at the very beginning of the 20-ft run. I am using the 8-gauge to future proof the install in case I need to install a newer, more powerful amp at some point. Thanks!

    Commenter image

    Buck Pomerantz from Crutchfield

    on 6/30/2021

    Dave, A fuse holder, and its fuse, must fit whatever size power cable is used. If you're using 8-gauge power and ground wires, then the fuse holder must be able to get attached to 8-gauge wire, and the fuse near the battery should be 50A or less. A great way to be sure you'll have everything you need to to get an amplifier wiring kit.
  • DRM from Tampa

    Posted on 6/13/2021

    Hi, I have been involved in wiring from high voltage- medium voltage 3 phase (A/C) data center, commercial buildings, ect. to low voltage house wiring and lower. I have found Crutchfield information to the point not complicated w/brain fogging stuff you dont need!

  • Jimmy cox from Theodore, al

    Posted on 5/20/2021

    Head has 2 line out Jack's, amp has 4 line ins. I'm trying to run 4 speakers from the amp. I tried splitters but the out put is weak. It's a jensen xda94rb amp, the control app is worthless. Much stress, please help.

    Commenter image

    Buck Pomerantz from Crutchfield

    on 5/21/2021

    Jimmy, If your receiver only has two outputs, you can use two RCA Y-cord adapters to make four input channels for your amp. I don't know what it is that you refer to as a "worthless control app", but I'll guess that the gain and crossover filters on the amp aren't set correctly. Check out this article for some guidance.
  • Vincent from SYLVANIA

    Posted on 5/1/2021

    How do I disconnect my battery to install my new amp?

    Commenter image

    Buck Pomerantz from Crutchfield

    on 5/3/2021

    Vincent, If your vehicle is electric or has more than one battery, you should only let a qualified mechanic or audio installer disconnect things. Otherwise, using an appropriately-sized wrench, you'd loosen the bolt-nut assembly holding the negative terminal to the battery's negative pole tightly. Then, you'd lift the terminal off the pole and tuck it away where it won't re-contact the negative battery pole. Then, the system is safe to work on without fear of short circuits, sparks, or shocks.
  • Anthony

    Posted on 4/30/2021

    Unusual setup for my Kenwood KAC-M3004. Installing on a motorcycle. Simple enough for the power wire, and ground wire. However, my ACC wire on the bike is connected to a 2 prong plug. One side goes to where it needs to go to give power when the key is turned on, the other side goes to ground...why would the ACC plug have 2 wires, with one going to ground?

    Commenter image

    Buck Pomerantz from Crutchfield

    on 5/3/2021

    Anthony, Without knowing the make and model of bike you're referring to, or seeing a wiring diagram of its electrical system, it's impossible to explain.