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Peek-A-Boo Harley Radio Tool Hack

In this article I explain a simple hack that allows you to use your smartphone as a Harley stereo system x-ray. This hack allows you to actually see the audio signal at multiple stages of an audio system. And I’ve made it Harley plug and play. I call it the Peek-A-Boo.This hack will work for any type of audio system but the cables and assemblies that I explain here are very specific to Harley stereos and are totally plug and play.

Important Disclaimer: American Hard Bag is not responsible for any support or mishaps that you may run into with this project. We provide this information as a free service for you to do with as you please. Use this information at your own risk. We have done our best to spell out every bit of information, details, and potential pitfalls that you might run into but we hold no responsibility for your actions.

The parts required to put together your own Peek-A-Boo can all be found on Amazon for under 50 bucks. I’ve included links to those parts as well as detailed instructions in the description below. The Peek-A-Boo takes all of the guesswork out of making system settings and tracking down problems.

Build Your Own Peek-A-Boo Tool for Under $50

With the Peek-A-Boo You Will Be Able to Get a Visual Display of the Audio Signal at Multiple Points Including:


  • Directly at the radio

  • At the DSP output

  • At the amplifier outputs

  • At the speaker terminals

  • Or even at the sound coming off of the speaker cone at the acoustic level


This gives you a full picture of exactly what is going on within a system. No more guessing. That’s for amateurs. There are about a hundred reasons why during a typical stereo system install on a Harley it would be advantageous for you to be able to connect to a specific point in the audio signal and get a clear on-screen display of exactly what the audio signal looks like at that stage of the system.Once you get used to having this tool, life will seem impossible without it. I mean, why would you ever work blind again? When for about 50 bucks you can make an adapter that allows you to see everything that’s going on in the system. Especially if you are a professional. I could talk for hours and write a book just on that subject alone.

How the XLR Interface Works and Why We Use It

You can make a Peek-A-Boo tool by connecting an XLR adapter to your phone. XLR is a three pin audio connector that is the industry standard connection type for the pro audio industry. It allows you to plug many different types of equipment together with a universal connection. XLR adapters for smartphones are designed to allow you to plug a very wide variety of audio devices right into your phone that range greatly in audio signal strength. And that makes XLR the perfect interface for this project, because they allow you to feed an unmodified audio signal directly to your phone and that signal can range anywhere from extremely weak and very low in level like the RCA outputs of your DSP to very high voltage such as at the amplifier output terminals without overloading your phone.

The XLR adapter has an internal battery powered circuit that isolates the signal from the phone and it automatically regulates that signal level for you. There are many XLR adapters out there specifically for smartphones but the one I have recently tested and found to be great for this project is the Smartrig ii made by Saramonic. I found this item on Amazon for $25 and it showed up the next day. It is important to get an adapter like the Smartrig that has a pre-amp built in and not just a passive 3.5mm to XLR adapter. A passive adapter would be dangerous for your phone.


Here is a link to the Smartrig ii that I use


Lightning Adapter for Apple Users

I am an iPhone user myself. So I found a Lightning port to 3.5mm headset adapter that I already had laying around. This allowed me to connect the XLR adapter to the microphone input of my iPhone. If you are an iPhone user. Be aware that most of the aftermarket lightning to headphone adapters that I have found on the market, do not support microphone input and will not work for this project. So I advise only using an actual Apple made adapter. They are almost the same price as the aftermarket units anyway. Also be aware that Apple certified and Apple made are two very different things.



Now that we have the Smartrig XLR adapter plugged into the phone our next task is to make a cable that can connect from the smartrig to the bike. And to do that we need to make a cable that is XLR on one end and Molex MX150 on the other end. The Molex MX150 series is the connector type that Harley uses throughout the entire bike for almost all of its circuits. The specific Molex connector we need here is a two pin male. That connector will allow us to plug into the factory radio as well as many of the plug and play cables that American Hard Bag makes. So we will endup with a single adapter cable that is very universal to many connections on the bike. 


The XLR microphone port on the Smartrig is female so you will need a male XLR end and wire to connect to a Molex brand MX150 series two pin connector. The easiest way to get this is to buy a basic short XLR cable and cut the female end off and strip back the wire for your Molex connections. 

Here is a link to one I found on Amazon

The parts that you will need for this hack can all be found on Amazon for under 50 bucks. You will need:


  • A type of app for your phone called an RTA or real time audio analyzer. Available at the app store for free or nearly free. Hundreds to choose from.

  • An XLR type microphone adapter for your smartphone

  • A short XLR cable that you will be cutting up to make your Harley adapter

  • An RCA cable that you will also be cutting up

  • A couple of Molex MX150 series connectors so that you can plug right into the bikes wire harness

  • And if you are an iPhone person you will need a lightning connector to 3.5mm headset adapter


The Molex brand connectors and matching pins are the most difficult parts in this project to find. These connectors are generally not available at local stores. They are however readily available on Amazon but you will also need to get a specialized crimper for these connectors . They do not work with standard wire crimpers. I have included specific Molex part numbers for all of the variations that you might want to get your hands on, as well as part numbers of the matching Molex pins.


Connector number

Pin Number

2 Pin Molex MX150 Male



2 Pin Molex MX150 Female



4 Pin Molex MX150 Female



At American Hard Bag we are not in the business of making these connectors for retail but we do have them and we will throw them in on an order at no charge if you are buying a system from us as long as you request them when you are making an order and not later down the road. We do not however sell them by themselves as a standalone product and at this point we don't have any plans to. Because of the required special crimper for these connectors when we supply these connectors, they will come with pins and wire pigtails already installed for you.

You will then need to make your own wire to wire connections to complete the project. We only supply the Molex connectors and we do not offer the XLR cable, XLR adapter, Lightning adapter, or a female RCA. Retailers of Velocity Speaker Design or American Hard Bag products can request these connectors at no charge with any order at any time.



The Molex connectors needed for this project are available from many retailers on the web but you will need a special crimping tool if you don't already have one. The tool I recommend is actually made for Delphi brand connectors but works spectacularly with the Molex pins specified here.

Here is a link to one I found on Amazon

Use a Molex MX150 series Molex part # 33481-0201 male two pin connector to terminate the wire side of the XLR cable. The male Molex pin part number is 33000-1001. Pin # 1 of the Molex connector should be red from the XLR cable and pin # 2 of the connector should be black (sometimes white) from the XLR cable.



Now the Peek-A-Boo is ready to plug in and use as is but there are two more simple adapters that we are going to want to make that will allow you to connect to additional parts of the bike. The first adapter you will want to make is a short female 2 pin molex to RCA cable. This will allow you to plug into any RCA connection. A good example of when you would need this is if you are using a sound processor like a Rockford Fosgate DSR1.

You will be able to plug into the RCA outputs of the DSR1 and clearly see the frequency response of the signal exiting the DSR1. You can then use the EQ and crossover of the DSR1 to flatten out or shape that signal before it makes it to the amplifier. Additionally you can also use a free oscilloscope app on your phone to check for clipping, noises and other types of distortion. I will make a dedicated article soon that covers that topic.

The important thing to understand is that now you have the physical connections to connect your phone to various parts of your audio system and there are all sorts of apps out there that you can use with your phone. Your phone is a very powerful computer and now you have many options that you did not have before. The last adapter that we want to make is a 4 pin female Molex with 2 two pin female Molex plugs on the other end.

This adapter will plug directly into your Harley radio’s rear speaker output as well as several American Hard Bag wire harnesses including our lid speaker wire harnesses. The adapter uses two separate 2 pin plugs so that you can choose to look at the right or left side signal. Or in the case of our lid speaker harness you can plug into the tweeter speaker lines or the 6x9 woofer speaker lines and see what's going on with each individual circuit. If you get your molex connectors from us with an order, we will have this adapter already assembled for you.


To use the Peek-A-Boo you will need to find an RTA app for your phone. RTA stands for Real Time Analyzer and it is an app that listens to the phone's microphone port and slices up the audio it hears into 31 bands just like the 31 bands of a standard equalizer that range from low frequencies to high frequencies so that you can instantly see any and all level differences amongst 31 slices of the sound spectrum. The RTA app that I recommend for the Peek-A-Boo is actually called RTA and is developed by Andrew Smith. This app is only available for iOS but fret not, there are lots of other RTA apps out there for Android as well.



Always keep the level knob of the Smartrig at zero and the switch to set to on while using. Swipe up and down on the RTA app to scale the sensitivity instead of using the knob on the Smartrig. Never set the switch to 48V. The 48V setting is there to power a microphone. Because we eliminated the ground wire from the XLR adapter this 48V power feature of the Smartrig is out of circuit, but turning on the 48V will generate 48 volts between the XLR connector body and either of the audio signal circuits within the XLR cable. So it is best practice to keep this feature (Phantom Power) turned off at all times. Don't use the Smartrig with the power turned off because this will actually eliminate the Smartrig's ability to regulate the signal voltage. It will function when turned off but don't do it anyway.



Any good RTA app will have a settings section that allows you to load a microphone calibration file so that any deviations in a microphone used with the app can be accounted for. When you buy a microphone that is designed for laboratory testing the microphone comes with this calibration file which is just a text file containing performance data for your specific microphone and formatted so that it conforms to an industry standard. When we use this app with the Peek-A-Boo we will not be using a microphone. Instead we will be physically plugging directly into the bike’s stereo system. But we still need to be concerned with the microphone calibration file because by default most RTA apps will load a calibration file for your phone's internal microphone, and that will totally throw off the accuracy of the app. So I have written a special calibration file that has a flat response for the microphone input. This file conforms to the industry format standards, so you should be able to use it with any RTA app.

You can download the flat calibration file here.

Copy and paste the entire contents into a notepad file and save as .txt. Then load that .txt as your calibration file in the RTA app. You will need to save this file in a place that is accessible from your phone. I like to use Dropbox myself.

For more information about how you use an RTA app check out the article I wrote called How to Use Pro Tune With A Harley Sound System. This article explains how to use an RTA app with our Pro Tune microphone kit and most all of the information in that article will directly apply to how you use an RTA app when using a Peek-A-Boo as well. You can find that article here. 



The last element that you will need is a pink noise test track. Pink noise is a test track that is specifically designed for use with an RTA. Pink noise has bursts of sound that are all equal in level and cover the entire sound spectrum. When viewed on an RTA, pink noise should show an equal level across all 31 bands. If there is any variation at any band, that band needs adjustment which can be done with your equalizer and other settings to bring that band up or down. In the real world the RTA never shows a perfect response but the goal is to get it as perfect as can be or at least to conform to your particular goals.



Now you can connect to any part of the audio system and instantly see what the frequency response is at that point. Connecting and using the Peek-A-Boo tool is now actually quicker and easier than any other diagnostic tool you own.  



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Peek-A-Boo Harley Radio Tool Hack

In this article I explain a simple hack that allows you to use your smartphone as a Harley stereo system x-ray

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