One of the most popular customization projects in cars is putting in better audio equipment.
Whether it’s upgrading the whole audio system or just putting in better speakers, upgrading the audio in your car is a very common project. This also makes it one of the most common projects to look at your car’s wiring, even if you’re normally not a car enthusiast.
One of the secrets of putting in new speakers, is that the final audio quality depends a lot on how the speakers are wired. While the speakers will technically still work when you mix up the positive and negative wire, the sound quality will not warrant the price you paid for your upgrade.
This is why it’s so important to test for the right wires. In this blog post, we’ll show you how to test for positive and negative speaker wires using a multimeter.
Aside from the multimeter you’ll be using to conduct the test, you also need a battery. This can be a simple (new) 9V battery. If you have some around, a piece of tape can save you some work, too.
If you’ve assembled the tape, battery, and multimeter, we can start testing. If you are looking for new multimeter -- look at the Best Automotive Multimeter 2018 review.
Set-up of an audio system
But first, we should familiarize ourselves with the basic set-up of an audio system. In the simplest systems, the car battery runs power to the amplifier.
This amplifier can be very fancy in custom systems and buried anywhere in the car, but most standard cars have the amplifier attached to the radio head unit (the thing that has the buttons you push).
Aside from the incoming power cable, the amplifier runs a phono/RCA cable to the radio head unit (integrated in a basic model), a ground cable away from the system, and speaker wires to each speaker.
The more elaborate your car’s audio system is, the more wires you’ll find, but the principles behind the system stay the same.
If you take a closer look at the speaker wires, you’ll notice that the speaker wires are a double wire. As you may suspect in this blog post, this is because each speaker has a positive and a negative wire.
The trick to hooking up a new speaker, or a whole new audio system, is to connect the positive and negative wire in the right place.
Measuring DC voltage with a multimeter
When you’re measuring voltage in a car, you always use the DC voltage setting on your multimeter. Batteries are always measures in DC, and because your car’s power is battery-operated, this is the one setting you’ll need.
Because measuring DC voltage is one of the core functions of a multimeter, there is almost no way your digital multimeter doesn’t have this setting. You can recognize it by the double-lined symbol, where the top line is solid and the bottom line broken up, so it appears as three dots.
To measure DC voltage, you’ll need to plug your standard test leads into the multimeter. To test your settings, you can quickly measure the car battery’s voltage. Hold each lead to a battery terminal and you should see a value of around 12V.
Here’s how to test a car battery with a multimeter:
How to test for positive and negative speaker wires with a multimeter
Now that we have a basic understanding of how a car audio system is set up and how to use a multimeter to test DC voltage, we can go ahead and go through the following steps to test for positive and negative speaker wires with a multimeter.
The first step combines a matter of personal safety and practicality.
Start prepping the workspace by disconnecting the wires from the outlet. It’s always a smart move to take a picture of the ‘before’ situation, so that plugging everything back in gets a lot easier.
Hook up wires to battery
Once you’re sure that everything is unplugged, get your 9V battery out.
Now, remove the speaker wires for one speaker from the receiver and from the speaker. On the receiver end, wrap each wire around one end of the battery.
Test wires with your multimeter
Now that the battery guarantees a flow of current through the wires, touch one wire with one of your test leads. If the test lead and wire’s polarities match up, you will see a positive reading on your screen.
This means that when your negative test lead touches a wire and you see a positive reading, you’re touching the negative wire. The reverse is also true. If you’re using your negative test lead and see a negative reading, you’re touching the positive wire.
Mark the wires
This is where your tape comes in. Mark the positive wire with a piece of tape and connect it to the speaker.
Now connect the negative wire and put everything back in place. If you now turn on the car’s audio system, your sound should be crystal clear!
It is not difficult to test for positive and negative speaker wires with a multimeter, but it takes a little bit of knowledge.
In this blog post, you learned the very basics of any audio system in cars, how to measure DC voltage with your multimeter, and how to combine that information to test for positive and negative speaker wires with a multimeter.
While it’s not a difficult task, you should take your time when you’re working with your car’s audio system. The steps above do not account for any time you’ll need figuring out what wires go to which speaker, or uncovering the wires or speakers themselves.
Especially for people who aren’t intimately familiar with car repairs, this can be a time consuming task.
Luckily, the first time will definitely be the hardest, and once you’ve gone through these steps the first time, you’re well on your way to become an expert in testing for positive and negative speaker wires.
3 thoughts on “How to Test for Positive and Negative Speaker Wires Using a Multimeter”
Wait. This isn’t testing the polarities of the wire, it’s just testing…. the battery to which you connected the wires prior to testing.
Yea – this description is lame! We want to know what wire is POS+ from the car amp to the speaker location so we can wire it accordingly! We already know to test the polarity of a speaker with a battery – C’mon!
I agree with Jonny. Take this post down. Or explain that the the only time you would do something like this is if your speaker wires do not have an indicator on the wire to show you which is which, you have lots of wire splices with different wires or are working with a wiring harness where the wires from your receiver are not color coded in the same way as the wires that go to your speakers.