1. Insert the banana plug of the measuring lead into the metal cap on the top of the test pencil to ensure good contact.
2. Clamp the alligator clip on the other end of the measuring wire to the ground (such as the metal casing of the car).
3. Pull the needle-like head of the test pencil into the inside of the wire insulation to be tested.
4. If the light-emitting tube in the pencil pen is lit, it indicates that the measured point has formed a loop, and the work is normal. Otherwise, the measured point is faulty and needs to be eliminated.