Video tutorial on how to make a cheap and easy temporary test light. If you have all the materials laying around, you should even be able to make this for free! This test light can be used to determine if you are receiving power at a certain area. This is a 12V application. The test light is unable to determine how much power an area is getting, but you will see if there is a drop in voltage if the light is dime or not as bright when it is connected directly to the battery.