Install and Wire Up Your Amplifier Like an Audio God

By December 3, 2014Audio
How to Install & Wire an Amplifier

After a bit of planning and research you finally got that killer amplifier and are on your way to transforming your stock audio system into a mobile concert arena! But looking at the pile of wires that come with the job, it becomes clear why some audio professionals charge the price of a few fancy steak dinners. It’s not that all audio installs are technically difficult, it’s more about the time involved to properly disassemble certain portions of the interior and run wires in a clean and concealed manner.

If you have an afternoon to spare and consider yourself a detail-oriented person, then this is one job you can rock out yourself. This guide assumes you’ve already selected a location for your amp and have it mounted. If you’re still deciding on an amp or don’t know where to put the one you bought, check out Planning Out Your Amplifier Install.

Depending on the placement of your battery in relation to your amp, the routing of wires may differ from our example which is based on the popular scenario where the battery is in the engine bay and the amp is mounted in the trunk. If you’re not comfortable splicing into wires there are a variety of wiring harness adapters for most if not all of these connections that allow you to plug in your wires without having to cut into your factory harness.


The items listed here may vary slightly depending on the amplifier and wiring kit you bought as well as your application – whether or not you’re keeping the factory head unit, speakers, etc.

1. Route & Connect the Power Cable

Unroll and straighten out the power and ground cables that came with your kit. With the higher quality kits, these cables often come with a ring terminal attached to one of their ends. If not, you’ll have to strip and crimp one on for each cable so that you can attached the power cable to the battery and the ground to a chassis bolt.

Remember to disconnect your negative battery cable from the terminal before you start any electrical work on your car. It’ll allow you to run power through the vehicle without the risk of a short circuit.

Getting Through the Firewall

Scan the firewall from both the outside and inside for a grommet that’s convenient to your battery. You may have to peel back the carpet in the interior for a better view. Look for an empty rubber grommet that’s covering an unused factory hole. That way you can just poke a hole through the grommet and run your power cable through.

If you can’t find one, then you’ll have to drill your own. Always start with a pilot hole to confirm you’re not going to spear anything on the other side. Once your hole is just big enough to pass the cable, protect the edges of the hole with some paint or rust inhibitor like POR-15. Don’t skip this step or you’ll have rust starting a party on your firewall!

Once the paint is dry, install a rubber grommet or firewall bushing into the hole to protect your cable from chaffing against the sharp metal edges.

Run the power cable through the grommet from the inside of the car with the ring terminal going towards the battery. It’s much easier to run a few feet of wire up to the battery from the inside rather than the entire length from the battery side. But if your power cable already comes with a fuse holder attached to it then you’ll have to go in through the engine bay otherwise you won’t be able to get the fuse holder through the hole in the firewall. As you route the cable inside the engine bay be sure the cable is far enough away from moving engine parts and anything that could pinch it.

Check to see if there’s a gap where the cable goes through the grommet. You don’t want water to run down the cable and into your car. Caulk any gaps around the inner edge of the grommet if necessary. Leave the power cable disconnected from the battery for now.

Installing a Fuse Holder

In most cases you’re going to have to cut your power cable near the battery to install a fuse holder inline with the cable. Most wiring kits come with the correct fuse and fuse holder but if you have to buy one separately, the fuse size depends on the maximum current draw of your system. You can usually find this information in the instruction manual, on the manufacturer’s website or by calling the product’s tech support line.

Look for a place to anchor your fuse holder within 18″ of your battery, although less than 6″ is best. This fuse plays an extremely important role in protecting your car from a fire if the power wire shorts out. The length of wire between the battery terminal and the fuse will be unprotected and that’s why you want this length to be as short as possible.

Once you decide on a good place to put the fuse holder, cut your power cable accordingly and sandwich the fuse holder between the ends. Use self-tapping screws to secure the fuse holder in place. Don’t put the actual fuse inside until the entire installation is complete!

You may now connect the power cable to the positive battery terminal (not to the battery post itself) by removing the terminal’s nut, slipping the power cable’s ring over the stud and replacing the nut.

Routing Through the Interior

The main objective is to conceal your wiring not only for safety but to give your install a clean and professional look. Always use the most direct route for your power cable and wiring. Depending on the location of the amp, you may need to remove the kick panel, pillar trim panel, door scuff plate, rear seats and pull up just enough carpet to facilitate the routing process.

Snake the power cable underneath the carpet or behind trim all the way to the amp while avoiding any pinch points like seat tracks or door jambs. At some point once you reach the amp, the power cable is going to have to come out from behind the trim or underneath the carpet to connect to the amp. A good technique is to cut a little slit in the carpet to allow the power cable to pop out right at the connection point.

2. Connect the Ground Cable

Your ground cable should be short and the same diameter (gauge) as your power cable. Look for a grounding bolt nearby. This can be any bolt going through the metal of your car. Scrape away any paint on the bolt and clean the grounding surface thoroughly to get better contact between the negative cable’s terminal ring and vehicle ground. Improper grounding is the primary cause of audio noise problems.

Slip the terminal ring over the bolt and tighten it back down so the ring is in good contact with the vehicle’s metal chassis.

If you can’t find a convenient ground screw or bolt, drill a hole for one. Be sure you know what you may be drilling into on the other side! This is especially important when you’re near the gas tank, gas line or brake line. An oops moment here could have you going through the tank, causing a spark and accidentally starring in the next Die Hard sequel – the “Ball of Fire” edition.

Whatever method you choose, always finish by covering the connection with paint or other rust-blocker to prevent corrosion. Cut a slit in the carpet like you did for the power cable so the negative (ground) cable can connect to the amp.

3. Run the Remote Turn-on Lead

The remote wire is responsible for turning your amplifier on and off in conjunction with your receiver or head unit. Whenever the receiver is powered up, it outputs voltage that travels down this wire to “tell” your amp to turn on too – your system won’t work without it.

Connecting to an Aftermarket Head Unit

Pull your head unit out of the dash so you can access the wiring in the back. Route your remote wire (usually blue) from the amp along the same path as your power cable and then branch off to go under the dash and to the back of your head unit. Aftermarket head units will generally have a remote turn on lead coming out of the back that you can splice into. Strip the insulation off a small section of this wire coming from the head unit, wrap the turn on lead you just ran from the amp around it and solder. Although soldering gives you the best and most reliable connection you can also use crimp connectors and a crimp tool to join the two wires. Remember to use heat shrink tubing around your soldered or crimped connection to protect it from damage or a potential short.

Connecting to a Factory Head Unit Without a Remote Wire

A common problem you’ll face is that most factory head units don’t have a remote turn on wire for you to tap into. If you’re in this situation, don’t worry, there’s still several other options to explore to get your amplifier working correctly.

Option 1: Tap into a Switched or Accessory Wire

This is the easiest and most convenient option, allowing your amp to turn on when the key is in the accessory or run position and then turn off when you shut off the car. It’s the same wire your head unit uses so grab a voltmeter or multimeter to probe the likely suspects until you identify it. Then splice into it as described above by soldering or using crimp connectors with heat shrink tubing.

Option 2: Wire an Inline Switch

If you want more control over your amp, installing a switch inline with your remote turn on lead will allow you to turn it off if you’re not listening to music while driving or waiting for someone in the car on a hot day and just want the air conditioning running.

Even when adding a switch, it’s still best to use a switched power source because if you tap into a constant 12-volt source and forget to switch off your amp when you park, you’ll come back to a drained battery.

Option 3: Enable DC Offset or Signal Sense Turn-On if Equipped

Some amplifiers have the ability to detect a 6-volt DC offset from the hi-level speaker outputs or sense the incoming audio signal when your head unit is turned on. If your amplifier has this feature, there’s usually a selector in the back allowing you to set the amp to turn on under one of these scenarios.

Option 4: Incorporate a Low Voltage Trigger Module

If your amp doesn’t have the features mentioned above, there are low voltage trigger modules that perform the same function that you can wire off your speaker leads. When voltage is present across your speaker, the circuitry inside the module produces a 12-volt output to the remote wire.

4. Run the Audio Cables

Making the audio signal connection between your head unit and amp is where it can get a little confusing for first-time installers. The method you choose will depend on two main factors: whether or not you’re connecting to a factory head unit and if your amp comes equipped with speaker-level inputs.

Connecting to an Aftermarket Head Unit

Working with an aftermarket head unit is the easiest scenario because it will already have preamp outputs in the back for you. Plug both of your RCA cables into the outputs in the back of your head unit and route them to the amp on the opposite side of the vehicle from the power cable and remote turn on lead. It’s important to separate audio signals from power wires to avoid potential noise problems.

Keep track of the left and right cables while routing. When you arrive at the amp, cut slits in the carpet, pull out both cables and plug them into the correct left and right jacks on the amp.

Connecting to a Factory Head Unit Without RCA Outputs

Like you may have already experienced with the remote turn on lead, factory head units don’t usually have RCA outputs so you’ll either have to convert the speaker leads into a low-level signal your amp can handle or use the speaker-level inputs on your amp (if equipped). Regardless the the option you choose below, always route audio signal cables on the opposite side of the vehicle from your power cable and try to steer clear of other factory wiring as much as possible.

Option 1: Line-out Converters (LOC)

If your amp doesn’t come equipped with speaker-level inputs you’ll have to buy a line-out converter (LOC) to convert the speaker output signal coming from the head unit to an RCA signal that goes into the amp. These are often called high-level to low-level signal adapters and typically run $10-$30.

The converter will typically have wires coming out of one side and 2 RCA jacks on the other. Simply take the wires from the converter and splice them into the matching speaker leads coming out of the back of your head unit. Then plug in your 2 RCA cables to the other end of your converter and run them to the amp. Make sure the connections on the converter are secure so they don’t come loose.

Option 2: Speaker-level Inputs

If your amplifier has speaker-level inputs you can use those instead of RCA cables or a converter. Splice into the speaker leads in the back of your head unit, run them to the amp and plug into the inputs directly (using appropriate connectors for your unit). The amp inputs convert the high voltage signal to one the amplifier can handle.

Another option many installers use is to splice into the wires for rear deck speakers rather than the back of the head unit since they’re so close. Not everyone amplifies their rear fill speakers and leave these connected to the head unit. But be sure your rear speakers get the full frequency spectrum and that your stock system doesn’t attenuate these speakers at a certain volume.

5. Connect Speaker Wires to the Amp

Now that your head unit and new amp are properly wired to each other, it’s time to route all speaker wires to the amp. Speakers should not be connected to both the head unit and amp because it will damage your electronics. If your speakers were being powered by your head unit in the previous setup, you’ll have to disconnect them.

The common exception are the rear speakers which are just used for fill or to tap into for speaker-level inputs for the amp. Although it’s a matter of personal taste, most people leave these connected to their head unit and concentrate on improving their front stage setup and adding a sub.

Wiring Aftermarket Speakers

Since you’ll be pulling out your factory speakers and will have to disassemble your door panels anyway, now is a good opportunity to run all new 16-gauge wiring from your new speakers to the amp so you’re sure to get the best sound possible. Although this isn’t absolutely necessary it’s definitely worth the extra time and minimal cost so you don’t have to take your car apart again in the future should you find yourself unhappy with the sound quality.

In an ideal setup you want to route all speaker (signal) wires so they stay clear of the power cable or other factory wiring but this is often easier said than done. To reach the front speakers, either route them like you did the RCA cables (or speaker-level lines depending on your application) or send them down the center console. This means that you may have to cross over under the dash and therefore use slightly longer wires to reach speakers on one side of your car. If you do have to cross a power cable or a bundle of factory wiring do it at a 90-degree angle so the cross-over point has minimum contact.

Your aftermarket speakers often provide instructions for a few different configurations depending on the brand, your car and number of channels on your amplifier so wire them according to the scenario that best fits your setup. Labeling your wires will help you keep track of your positive and negative terminals.

Wiring rear speakers is easy because they’re close by but front speakers can get tricky when you need to get into the door. A good trick for fishing new speaker wires through the rubber boot and into the door is to snip the factory speaker wires under the dash before they go into the boot and tie your new speaker wires to the ends protruding from the boot. Make sure they are tied securely so they don’t come apart. Then gently pull out the factory speaker wires from the other side (door side) and your new wires will travel through the boot and up to where your new speakers will be.

Wiring Factory Speakers

People often upgrade their audio system in stages so you if you’re hanging onto your factory speakers it’s much easier to tap into the factory wiring that’s already under the dash for the front speakers. Run new speaker wires from your amp as described in the section above for aftermarket speakers and splice each one into the corresponding factory wire in the harness under the dash before they go into the door boots.

6. Test Your New Amp

With all your connections in place, insert the fuse in the fuse holder near the battery, reconnect the positive terminal first followed by the negative battery terminal. Start the car and make sure your electronics are working properly. Turn on your radio and set the gain on the amp. Listen for noise, static or alternator whine when you rev up the engine. If all you hear is the sweet sound of guitars wailing, bass thumping and vocals howling then you just rocked through this install like an audio god!

7. Secure All Wiring & Reassemble The Interior

Fully re-install your head unit being careful not to pinch or pull apart any wires in the back. Look over all your wiring including the power cable and use zip-ties to secure everything in place so they don’t get pitched or interfere with other moving parts. Replace the carpeting and interior panels and finally check that your amp and sub are securely attached to their mounting areas. In an accident, amps and subs can become dangerous projectiles.

Photo credit: AutoSound

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