This is a very simple yet very useful little gadget. Anyone can make it for 1$(or less). This is really good for beginners and it can help you troubleshoot. Yes you can buy one ore use the multimeter, but whats the fin in that?

Step 1: Parts You Will Need

1x 3 volt battery pack
1x Light Emitting Diodes (also known as LED)
2x Something for the probes(ex. Alligator clips, plugs)
Optional is something to put it in(I used a speaker grill that i had laying around, It looks fancy :) )

If you want to make a multi channel one like i did you are gonna need as many times LED's and Plugs(or whatever you are using)

Step 2: Assembly

Here is the schematic
And there is another picture for those who are just starting

Step 3: Optional Adding a Case and Finishing

I added a cheap computer speaker grill i had laying around so i used that. I drilled the holes for everything and added the parts. There is a picture of it finished. I used hot glue to secure the bat pack and the wires. To use this device connect the wire/cable to one probe and the other probe to the other end of the wire, if the led lights up your good the wire/cable is good. to make a multi channel one connect the circuit in parallel

All done enjoy

Sorry if my English isn't the best
--Valentin