1. Connect one of the test light probes to the negative battery terminal or vehicle ground.
2. Connect the second probe to a connection in the circuit being tested, preferably located as close to the battery or fuse as possible.
3. If the test light comes on, voltage is present: this means that the part of the circuit between the connection and the battery is OK.
4. Continue checking the rest of the circuit in the same manner.
5. When you find a point where there is no voltage, it means that the source of the fault lies between this point and the last point where voltage was present.
6. Most problems are caused by poor connection.
The article is reprinted from a web resource: mitsubishiman
Attention! Remember that in some circuits voltage is present only if the key in the ignition switch is turned to a certain position.