You can see the kit comes with three parts to it, obviously the tester itself here, the alligator clip that will actually go on to the end here. You also have the hook that goes over the end which goes around the wire and pierces the wire to test the wire also. This is the larger alligator clip you use for the ground. The way this unit identifies the circuits working, it does it in two different ways, it actually lights up and it actually makes a sound. We will demonstrate that here with this light we have hooked up to a power supply. This is the ground so this will go to the ground of one of the lights that you are working with. This probe here will actually go to the wire itself. We will use our hook here, and we will go ahead and just test the wire. Just squeeze it gently and you hear a tone and it lights up. What is also nice about this, if you actually reverse the polarity of this, it will reverse the ends and tell you the polarity.
We will use the small alligator clip here. We will attach it to our ground here and our original ground to the power supply here. You can see it just lights up, so that tells you that would be the ground and this would be the power wire. It helps determine the polarity, if you are not sure which end of the circuit you are on. You can see this is a nice heavy duty unit, these are the ones we use in our own shops, and that is what you have for part # 40376.