Connecting your car speakers to an amp
Tip: You can use your vehicle's factory wiring
Buck Pomerantz was born and raised in Philadelphia. His parents bought their first television set when he was born. He figured out how to run it by the time he was two. Besides athletics, his formative interests included electronics, amateur radio, music, and stage crew work. He got his BA in writing from Brown University. Then he joined a rock 'n roll band as their soundman and moved to Charlottesville, Virginia. After that venture failed, he spent time in Boston, New Orleans, and Berkeley. He worked in a music store in Austin manufacturing, installing, repairing, and operating sound systems for recording studios, clubs, and bands. He moved back to Charlottesville, ran a little recording studio and finally joined Crutchfield as a copywriter. He has 2 grown children and 3 grandchildren, but after a good nap he can still rock out.
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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.
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?
In this case, you don't use the speaker wires on the stereo's wiring harness. 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. Remember, you're sending the audio signal to your amp through the RCA cables. And yes, fade and balance controls will still work fine.
The adapter harness that connects your stereo to the car's wiring has speaker wires that would normally connect to the stereo's speaker wires (if you weren't using an outboard amplifier). You'll connect the amp's speaker output wires to those. That's the real trick we're talking about here.
What you're seeing here
Normally, if there were no external amplifier, 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 also adding an 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.
Meanwhile, the RCA cables carry the audio signal to the amplifier and the blue wire from the stereo plug turns on the amp whenever the stereo is turned on.
Using those wires on the adapter harness to send the audio to the speakers is how you avoid having to run new speaker wiring throughout the car. That's the bottom side of the triangle in the photo — speaker wires from the amp connect to the speaker wires on the adapter harness. Then that harness plugs into your car. 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 new speaker wires at the same time.
EFX 9-wire Ultra Flex speaker wire
Some products to help you do it
Crutchfield offers a 12-foot and a 20-foot 9-wire cable that helps simplify running eight speaker wires plus a remote turn-on lead from your amplifier to the rear of your receiver. We also carry a small selection of highly conductive, pure copper speaker wire, available by the foot, that will also work well for sending the amp's output signal to the factory speaker wires.
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 over 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. 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.