How To Install a Car Amplifier

Amplifier Installation

Amplifier Install Guide

Difficulty: Moderate
To get the full effect of your car's audio system, you may want to install a car amplifier to power the speakers. Additionally, if you wish to use subwoofers you will need an amplifier to power them. Installing a car audio amplifier yourself is a fairly simple task that will save you money on your car stereo system. This guide shows you how to install a car amplifier for either of the above purposes.



  • STEP 1: Choose where to put your new amp. If you are installing subwoofers it is usually best to put the amplifier in the trunk next to or attached to your subwoofer enclosure. If you are going to power your main car speakers with the amplifier then it may be better to put the amp under the passenger's seat.
  • STEP 2: Purchase the following wiring for the amp: a thick power cable (the thickness required depends on the total wattage of your amp, ask a sales rep or consult your amplifier's manual for the proper gauge) that will have to reach from your battery to the amp (the power cable should also have an inline fuse to protect the amplifier); 3 feet of ground cable of equal thickness as the power cable; an RCA signal cable to carry the left and right signals from your head unit to the amp; a "remote on" wire which can be any thin wire (20 to 24 gauge) that will also run from the head unit to the amp; speaker wire (if you are powering subwoofers you should only need about 3 feet of 12-gauge wire per sub, if you are going to power your main speakers you will need enough 16-gauge wire to reach each speaker from the amp, 12 feet per speaker is usually safe).
  • STEP 3: Gather the following tools: screwdrivers, wire cutters, wire strippers, pliers, a utility knife, sandpaper, masking tape and a pen for labeling, 2 crimp on o-ring ends for the power and ground cables, and if you are hooking the amp to your speakers 2 crimp on female spade connectors for each speaker.
  • STEP 4: Find a manual with instructions on taking off the dash of your car (not the whole dash -- just the head unit, in order to hook wires to the back), and also to get at your car's speakers if you are hooking the amp to them.

Tips & Warnings

  • The head unit is your cassette or CD player that sits in the dash of your car.
  • If your head unit is very old or is stock, you may not have RCA outputs in the back. In this case you will need an amplifier that has "speaker level" inputs and you will attach the lines that come out of your head unit and would normally go to the speakers to the amp instead.
  • Read the manual for your amplifier, it will give you all sorts of helpful information like the proper gauges of wire and what fuse to use.
  • Stock speakers are not meant to handle the power put out by a car audio amplifier. If you hook the amp to your stock speakers you will probably blow them.

The Installation


  • STEP 1: Disconnect the ground (negative) cable from your battery. NEVER work on the electrical system of your car with this connected.
  • STEP 2: Attach the side with the fuse of the thick positive (+/red) power cable to the connector on the positive terminal of your battery; the o-ring can be sandwiched in the bolt on the connector that connects your car to the battery. Now put the fuse in the fuse holder.
  • STEP 3: Run the power cable through the firewall of your car (there is usually an opening on the driver's side) and to your amplifier. If your amp is in the back it is usually best to run this wire under the plastic molding that goes along the bottom edge of your car. Be careful where you run the wire because the power cables should never be near the signal or speaker wires.
  • STEP 4: Find a metal bolt or screw on the metal of your car near the amp to connect the ground cable to. This should be as close to the amp as possible, never more than 3 feet. Unscrew it and clean the metal surface with sandpaper. Attach the ground to it with the o-ring and screw it back down firmly.
  • STEP 5: Remove your head unit and run the signal and remote on wires from behind the head unit to your amp. Connect the RCA connectors and the remote on wire to the back of your head unit.
  • STEP 6: *If you are installing subwoofers and not running your normal speakers off the amplifier skip to step 7* Run the 16 gauge wire from each one of your speakers to the amplifier. On the amp side use the masking tape to label each wire so you know which speaker it is. On the speaker end strip a 1/4 inch off the ends of the wires and crimp on the female spade connectors with your pliers. Connect the spade connectors to your speakers making sure to match the positive (+/red or white) with the positive terminal and the negative (-/black) with the negative one.
  • STEP 7: Connect everything to your amplifier. Only strip off as much as you need off the end of each wire to make a solid connection, you do not want any exposed wire hanging out. If you have subs, attach them to the amp with the 12 gauge speaker wire.
  • STEP 8: Secure your amp to something. If it is in the back you can screw it directly to your subwoofer enclosure. If it is under a seat you may just want to get some straps that hold it down.
  • STEP 9: Reconnect your car's negative cable to the battery. Test your system and make sure everything works, going around to see that every speaker is on before you put everything back together.
  • STEP 10: Put everything back together.

Tips & Warnings

  • The most common cause of an amplifier not turning on is a bad ground. If the amp isn't working try a different spot to connect the ground cable to.
  • Never EVER work on the electrical system of your car with the ground wire attached to the battery. You can damage yourself and your equipment.
  • Never have your speaker or signal wires run near your amplifier's power cables. If they must cross do so perpendicularly and only in one spot.

The one thing that has costs us most of our time and money is "temporary" wiring setups. Back when we didn't know any better, and started to learn about better ways of doing things we called them upgrades. If you are serious about your system and its performance, or are thinking of adding on later; here are a few tips that can help you out with both time and money in the long run.

Run your wiring once.
Think ahead.. are you adding another amp soon? a second amp or replacing the one you have with a larger one?
If so, go ahead and spend a little extra on larger wire and maybe a distribution block. Wiring kits are cheaper than individual components (wires, terminals, distribution blocks, RCAs, fuses, etc), and you are getting almost everything you, no last minute runs back to the store to pick up one or two things you forgot, or worse-taking a shortcut and leaving something out.

Use fuses where recommended.
A car full of smoke is dangerous and embarrassing. Put a fuse as close to the battery as possible when running power wires to the back of the car. This will prevent damage if the power wire somehow grounds out before it reaches the amps. If you use a distribution block, use an inline fuse from there as well.

Run your RCAs together, but away from power wires. Most quality amplifiers now have RCA inputs for every channel, so upgrades can be as simple as plug in and play. Use shielded RCA cables. An unshielded RCA cable is almost like an antenna, once the signal reaches the amplifier it has picked up alot of noise, and will inturn be amplified as well - causing alot of grief. A good shielded RCA is well worth the money.

Lastly, designate a good ground for your equiptment in the back. Use the same size wire to ground your system as you use to feed it. I like to use seat belt bolts to ground mine. Where ever you decide to ground your system, brush or scrape off the paint in that area to ensure a good metal to metal connection, and tighten the bolt back down tight.

Do it right the first time, and there won't be any extra time and or money spent on upgrades to your power or wiring.

Determine the RMS power rating of an amplifier

Class D amplifiers are generally 80-90% efficiency
Class A/B amplifiers are 50-60% efficiency
Class T or Digital amps are close to 90% efficiency

As mentioned earlier, to find the true output of an amplifier, we need to know the actual DC input voltage, current draw and efficiency rating. We can roughly determine the peak output power of an amp, then with a little math... (Ohm's Law) we can estimate the RMS power of same.

Let's run some numbers on a popular Class D amp: JBL BP600.1

Voltage Source: 12.9 volts/specs (assumed)
Peak current draw: 57 amperes/specs (2 x 30A. fuses)
Class D Circuitry (eff % > 0.816)
RMS Ratings: 300 RMS @ 4 ohms, 600 RMS @ 1-2 ohms (specs)

The Math: (Ohm's Law)

Volts x Amps = Watts (this is peak or max rating #)
12.9 x 57 = 735.3 watts (peak draw) DC input
RMS/735.3 = .816 eff. rating

RMS power = peak watts x eff. %
735.3 x .82 = 600 RMS @ 1-2 ohms (300 RMS @ 4 ohms) RMS AC output

OK, that's the scoop. We did fudge a bit to determine the efficiency rating number. But we do know that the minimum output specs for this amp are 600 RMS into a 1-2 ohm load. We also know that this Class D amp is above 80% eff.

To really dial this in perfectly, we would need a regulated DC power supply source, a fixed load resistor, a calibrated input signal (1-4 volts AC) source, an AC/DC voltmeter and an ammeter to measure voltage and amps at the load resistor. Having all this test gear, we can then make a precise output measurment of a given amp.

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