Wiretester
And then a thought came to me. Simple but effective. And nobody on the original staory noticed it !! Ok what am I talking about ???Well we made a simple polarity tester. It tests which side of a battery or power supply is the ground and which is the positive lead. You can find how to build it by clicking here.
Now I thought that there is another purpose for this really clever tester. You can use it as a wire tester.
This picture shows how you can use this if the wires go into (for example) another room. Just put a battery on on end of the wires and the polaruty tester on the other side. it does not matter on which wire you put the positive lead of the power supply (or battery) and on which wire you put the polarity tester leads. If the wires are not broken one of the leds will be on.
And this picture shows how easy it is to use the polarity tester as a single wire tester.
A real multipurpose tool is this polarity tester.