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.

Can mono jacks be used?
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. <br> <br> <br>link to picture incase it didn't show up: <br>https://lh6.googleusercontent.com/-Fy237GaGunU/UAgsBglrvHI/AAAAAAAAAFk/u3jajxuXJF8/s640/help.jpg
Thanks, really cool project and useful. One thing you may want to add to the &quot;parts&quot; list is the SPDT switch? I may have missed it but I don't think it's on the list now. <br><br>Again, thanks for the posting!
can i use 1k resistors instead?
not with 9v
What if your cable testers inputs break?
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&quot;. With this I can teste 1/4&quot; to 1/4&quot; cables (both mono and stereo), XLR to 1/4&quot;, 1/4&quot; to XLR and XLR to XLR.<br /> Thanks a lot
that's great!&nbsp;do you have a link to a good pinout of an 1/4&quot; to XLR cable so when I&nbsp;add xlr, I wire mine up in a way that makes sense?<br />
No, I simply connected the 1/4&quot;&nbsp; (stereo plug) and the XLR at the same time. (n&deg; 1 of 1/4&quot; with n&deg; of XLR ...)
Very simple idea.&nbsp; If you make it smaller, you could probably sell it and make lots of money.<br />

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Bio: 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 ... More »
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