What Do the Red and Green Lights on an Automotive Test Pen Indicate?
2 Answers
Automotive test pen red and green lights represent respectively: the red light indicates an increase in voltage, while the green light indicates a decrease in voltage. Below is relevant information about automotive test pens: Definition: An automotive test pen, also known as an automotive voltage tester or test light, is a commonly used circuit testing tool for automotive electricians during activities such as installing additional electrical components, modifying circuits, and performing repairs. Function: It is used to detect whether there is voltage at the test point in an automotive circuit. For precise measurements, a multimeter is still required. Structure: An automotive test pen consists of a barrel; at the front end of the barrel, there is a metal tip called the probe, which is used to contact the test point; inside the barrel, there is an indicator light (a small bulb or LED); at the rear end of the barrel, there is a wire with a clip attached. Some automotive test pens also include a fuse.
Last time when repairing the car, the experienced mechanic taught me how to use a test light: A green light indicates the circuit has power but isn't grounded, suitable for testing the output end of a fuse. A red light means a positive power source is detected, like when directly touching the positive terminal of the battery, it will turn completely red. If both lights come on together, it's most likely a pulse signal, such as the injector circuit which often flashes this way. When there's a loop but unstable voltage, it will also breathe and flicker. For ground wire detection, only the red light should be on, which is a point often confused by beginners. If the red light is on alone, it's mostly directly touching the positive terminal. A green light alone suggests detecting a floating voltage. In actual repairs, combining it with a multimeter is more accurate.
