Connecting your car speakers to an amp

Sending the audio signal from a receiver to a 4-channel amplifier's inputs via RCA cables or the amp's speaker-level inputs is straight forward and simple enough, but getting the amplified signal back to the speakers—well that's another matter.

This article discusses adding an amplifier to an aftermarket stereo. For tips on connecting an amplifier to a factory stereo, read this article instead.

Getting signal to the speakers

The speakers are usually in four different corners of your vehicle, and running separate new speaker wires to each one presents many challenges, including how to get the wire past the car door hinges to the front door speaker locations.

A convenient way to send the powered signal from your amplifier to your speakers is to run the speaker wires back to the harness behind your stereo, where all your car’s speaker connections are accessible in one place.

Which speaker wires go where?

Normally, when you install a new stereo, all the wires from the stereo would connect to the car wiring adapter. The wires would run from one black connector to the other (the right side of the photo below).

But since we're using an external amplifier for the speakers, the speaker wires from the car get diverted to the amp — that's the bundle of wires on the bottom plug heading left to the amplifier.

The speaker wires from the new stereo aren't used. You can either cut them off (like we did in the photo below) or just tape them up – each wire individually – so that none of the wire ends can touch anything else.

Meanwhile, the RCA cables carry the audio signal to the amplifier and the blue wire from the stereo turns on the amp whenever the stereo is turned on. And yes, fade and balance controls will still work fine, so long as you connect the RCA cables correctly.

Running the amp's output wires to the speaker wires on the stereo's adapter harness is how you avoid having to run new speaker wiring throughout the car. That's the bottom side of the triangle in the photo above — speaker wires from the amp connect to the speaker wires on the adapter harness. Then that harness plugs into your car. The diagram below is a more detailed depiction of the layout.

For 4-speaker systems, you'd need to make eight connections — a positive and negative wire for each speaker. This means, you just need to run the eight speaker wires from the dash to the amplifier, just like you do the RCA cables. In fact, when you're installing the amp, it's smart to run the RCA cables and new speaker wires at the same time.

Some products to help you do it

Our favorite option is the Crutchfield 9-wire cable shown above because it helps simplify running eight speaker wires plus a remote turn-on lead from your amplifier to the rear of your receiver and each set of speaker wires is color coded. We also carry a small selection of highly conductive, pure copper speaker wire, available by the foot, that will also work well, if you don't want the 9-wire, all-in-one solution.

A multi-pack of Posi-Products Car Stereo Connectors could come in handy here, so you can make all the speaker connections without having to solder anything.

High-power amps need bigger wires

For amplifiers with more than 75 watts RMS of output per channel, it may be better to go ahead and run new 14- or 16-gauge speaker wires directly from the amp to each speaker.

Factory speaker wires are very thin, with high electrical resistance, so they can cause noticeable power loss when higher wattages try to get through. But amplifiers of 75-watts or less aren't really affected by this, so running their outputs through factory wiring remains a practical and convenient solution.

Let us know what you need

This article focused on a way to simplify the speaker connections when using an aftermarket stereo. If you're connecting an amplifier to a factory system, check out this How To guide for tips. For information about other aspects of amplifier installation, like power and ground wiring, check out our Amplifier Installation Guide.

If you have any questions about connecting a new amplifier to your speakers, contact our advisors via chat or phone. They'll take the time to answer your questions and explain the details, then get you set up with whatever you need.