By far one of the simplest diagnostic tools out there when working on cars is a test light. These handy little tools help light up the situation when trying to find out electrical problems. 

In its simplest form, the test light is just a light bulb that will energize when receiving power. A test light is shaped like a screwdriver, but instead of a flat head or phillips tip, they have a sharp point. The other major differences include a clear handle that holds the bulb, and a wire coming out of the handle that gets clipped to a ground. To use a test light, you simply clip the ground wire to a good ground; then with the sharp point you touch a contact, if the bulb lights up then you have power. If the bulb doesn’t light up, then you don’t have any power. The sharp point of the test light can also be used to puncture the casing of wires. 

There is a ton of different ways to use a test light. If you want to test to see if a fuse is good, you can touch the bare metal on either side of the fuse. If only one side lights up the test light, you have a bad fuse. A test light can be used to find a broken wire as well; poke the sharp point into the wire and when the bulb doesn’t light up, you have found your break. If a tail light or any other bulb fails to light up and you’re not sure if the bulb went bad or if you’re not getting power, you can pop the test light probe into the connector and see if it lights up. The other ways to use it is simply just checking wires to see if they are getting power when they are supposed to, like an ignition switch or any other hot-in-run wires. 

Test lights are a cheap, readily available tool that can be found at any auto parts store. For a few bucks you can have one sitting in your tool box and save yourself hours of frustration!