How To Test A Car Amplifier With A Multimeter

MultimeterFinding out how to test a car amplifier with a multimeter may sound like a sophisticated task. However, having the right tools can save you lots of hassle, as well as time and money. It represents a routine operation, especially if you have all the tools at hand. There are, however, a few key elements to take in consideration before you even start. So, how do you test a car amplifier with a multimeter? What is the right time to give up on fixing things and call a mechanic instead? Here are the answers to all your questions.

Long story short, you will have to locate the amp or amps, as you might have more than one, then hook the multimeter in and run a test. Different multimeters come with different features, yet their operating principles are the same. Based on the result, you have a diagnostic that allows you to make a decision. You can either perform a simple repair or fix an element or you can call your mechanic. However, performing the test yourself will avoid the extra expenses of professional diagnostics.


Testing, Preparations and Expectations

These days, automotive stereos are more complicated than ever. If you remember the good old days of older cars, you can probably remember those sweet single speakers that were mounted on dashboards. Testing those was a matter of seconds. Today, if somehow your eight speaker audio system fails on you, you better arm yourself with plenty of patience. While the whole task can be quite frustrating, it is still doable and can save you money.

If the main unit works and lights up, the problem might be associated with external amps. Keep in mind that not all cars rely on amps – depending on the model and manufacturing year. How can you tell? Check the manual. If this is not the case, testing the amp will tell you if it gets enough power. If it does not, it will not let the music go through to speakers, hence your problem.

Configuring the Multimeter

Configuring the multimeter is not so complicated, even if you are new to this. The black probe must go into the common socket (sometimes labeled COM). The red one goes in the socket labeled A. A stands for amperage. You might find two different sockets – one is more sensitive, while the other one is high amperage. If not sure which one to try, use the socket with the highest rating.

Turn the central dial of the multimeter to the amperage setting corresponding with the socket. There is a small chance these settings look different, yet they mean the same thing. You might find A and mA settings on both the amp and multimeter, but you may also find just one A setting on the dial. If confused, double check the manual.

Testing the Amplifier

Locating the amp is the first step in the process. It might be anywhere – in the boot, under the dashboard, behind one of the seats and so on. The manual should tell you precisely where to find it. Once you find it, check the wiring diagram It will tell you which wires must be tested, as well as the characteristics they should have.

If your amp has more than one plug, you will need to consult the wiring diagram again and identify the main one. It is usually marked 12V+. It could be hot at all times or only when you run the car. Turn the key to ignition to figure that out.

While no one likes problems, ideally you should find the issue to be here. If it is not hot but the system is still not working, you will need to trace all the wires and look for a break or a problematic plug. This could be extremely frustrating and time consuming.

Tips and Helpful Advice

It is highly recommended to turn off the power before the meter is connected. Why? Easy! When the power is on, current will go through the circuit instantly. The probe lead is small and covers a small area, so it might heat up and weld itself to the amp.

Alligator clip leads are a good idea too. The high current can damage the probe due to its small surface. If you attach alligator clip leads, the current is then distributed over a wider area. The risk of damage is extremely low then. Of course, the power should be off while you attach them.

Issue #1 – The Amplifier Does not Turn on

Check the fuse by the battery, as well as both sides. You cannot perform this diagnostic by looking. Sometimes, fuses are bad, but not blown. You might have to change a fuse, check the remote wire or check the voltage at the amp terminal.

Issue #2 – Amp Goes on into Protect Mode

Disconnect everything and turn the amp back on. If it still goes into protect mode, it has a problem. If not, reconnect your speakers. Going back into protect mode means the speakers have a problem. It could be the wiring as well.

Issue #3 – Amp Goes on Without Output

Go through all settings, as well as all volume levels. You might have to use an alternative input for testing.

Issue #4 – Output Is Distorted

Clear all the variables and try all the settings again. There is no other way to figure out where the problem might be.

Issue #5 – Low Output from the Amp

Turn the volume down, as well as the subsonic filter. Go up again, down again, check the radio as well. The voltage drop at amp terminals will give you the issue. If it stays over 12V, speakers must be checked.

​​Issue #6 – Amp Goes on and off

Run the system until the amp goes off and double check the voltage. If it goes under 10V, go through the wiring.


Bottom line, testing a car amplifier with a multimeter is relatively simple for someone with a touch of passion for technology.​


  1. Hello, I’m really confused as to why my car sub has stopped working, I have a Rockford fosgate p3 punch sub with a capacitor and a jl audio 500w mono amp. The amp turns on but doesn’t go into protect mode, the capacitor turns on and reads 12.3-12.4 but I have no sound coming out of my sub. I’ve gone over my wiring and everything seems fine, I’ve checked all the fuses and they’re ok as well. I’m just trying to figure out why I have no sound coming out my sub, o yea, I also did a test on the sub and it works just fine. There’s no hissing or anything like that. When I turn my car on the radio works I just have no bass

  2. I have a amp my speakers sound fine through it but when I hook up my subwoofer it sounds distorted and barely has any sound can you tell me what it is its a 4channel amp I’m hooking up the woofer to the rear two channels left and right pos and neg terminals.

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