- Indicator light: the top of the tester lights up brightly when the circuit is okay, indicating the circuit state. The green light indicates positive polarity and the red light indicates negative polarity. - Probe and alligator clip: the long probe with an alligator clip ensures you reach the right place. The sharp steel probe can pierce the cable insulation with ease. - Multi-function tester: ideal for checking various vehicle circuits, quickly checking car headlights, taillights, turn signal circuits, defective sockets, fuse connectors, etc. - Suitable for: Professional 6-24V Circuit Detection Test Pen is ideal for checking circuits in cars, trailers, boats, motorcycles and other low voltage systems. - Practical applications: use on car lighting circuits (headlights, taillights, turn signals) to verify operation; diagnose defective sockets and fuse connectors; check trailers, boats, motorcycles and other low-voltage systems for circuit integrity.