16 The basic test light can also detect current flow besides the aforementioned voltage and ground testing. Simply connect the test light between the battery terminal and cable clamp as shown to detect any current flow that could be causing a battery drain. Ensure the key is off and doors are closed. If you have a measurable drain, look for sticking console or glove box lights, or bad electronic hardware. Pull your fuses one at a time until the light goes out and you’ve found your circuit causing you problems.