DIY Guitar Cable Tester




About: my name is Joe Wozniak and I sing, play guitar, mandolin, keyboard, and various circuit-bent things in the band Rooftop Ridicule. It's very likable stuff and the circuit-bent things are used very tastefully,...

Hello Wozn here from the band Rooftop Ridicule. Today I'm going to help you make a quick simple cable tester that's already saved me much time and heartache. You don't realize until you have one how useful it is to confirm in a second whether a cable is trustworthy or not, not to mention handy. You can't always be sure with an amp and a guitar when input jacks are so often the culprit, you may think you have several bad cables, and sometimes you're right. This way you can confirm or rule-out the cable for sure.

Step 1: Gather Parts

you need:

two stereo 1/4" jacks
three leds (recommend: 1 red 1 green 1 yellow 'cause that's rasta)
three 330ohm resistors
a little speaker, from say a clock radio or something, this is OPTIONAL
9v battery clip
9v battery holder
9v battery
a box

thats it my friends!

Step 2: Check Out the Schematic

Not to complicated right? basically electricity is constantly flowing from the tip of one side of the cable to the tip of the other side and lighting the "tip" light.

If the switch is off and only the tip light is on, that's good.

The ring or ground light should turn on also when the switch is flipped toward one or the other, or both will turn on either way if it's a mono cable. If they don't, one of them is disconnected, and that's a bad cable.

With the switch off, if the tip is shorting to ground or the ring, one or both of those lights will come on with the tip light when you wiggle the cable, even though the switch is in the middle. you know then that it's shorting inside and that's a broken cable.

No lights, or no tip light even if the other two come on with the switch, and it's obviously a bad cable too.

Note: two simple adapters can be made really easily to make this test XLR cables as well, or XLR jacks can be added. it doesn't necessarily matter which conductors you connect to which light, as long as they are the same on both sides and you know which is which. In this case you may even want a SP3T switch instead. If you used a three way switch you could test just one of the three conductors at a time and any two lights lighting would mean a short between them. These are harder to find and not really necessary, but would make the thing a little less confusing to use.

Step 3: Assembly

You can see I used a pretty standard RadioShack project box, and a barely big enough one at that. I would recommend something larger and frankly it can even be cardboard. If you are clever and get the right jacks you could go smaller, say Altoids tin would be nice.

The nice thing about this setup was that the leads of the leds being soldered to the jack helped hold them in place as well. I did add glue as well. I also shaved off the dome of the leds for looks and so they wouldn't get pushed in.

Step 4: Test Yourself a Cable!

Time to test some cables! check out the video to see it in action.

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    10 Discussions


    6 years ago on Introduction

    I added a photo showing what I have done. When I plug in guitar cables and click on, in one direction the light comes up green. None of the other lights work even with bad guitar cables. Now when the light does turn up green the cables are in working condition which i like green means go. but something is obviously wrong here. I spent all the money for this and soldering iron. Please help.

    link to picture incase it didn't show up:


    7 years ago on Introduction

    Thanks, really cool project and useful. One thing you may want to add to the "parts" list is the SPDT switch? I may have missed it but I don't think it's on the list now.

    Again, thanks for the posting!


    9 years ago on Introduction

    Very easy and useful project. I did it almost the same way, but also added two XLR jacks (male and female), attached to the 1/4". With this I can teste 1/4" to 1/4" cables (both mono and stereo), XLR to 1/4", 1/4" to XLR and XLR to XLR.
    Thanks a lot

    2 replies

    Reply 9 years ago on Introduction

    that's great! do you have a link to a good pinout of an 1/4" to XLR cable so when I add xlr, I wire mine up in a way that makes sense?


    Reply 9 years ago on Introduction

    No, I simply connected the 1/4"  (stereo plug) and the XLR at the same time. (n° 1 of 1/4" with n° of XLR ...)


    Very simple idea.  If you make it smaller, you could probably sell it and make lots of money.