What is the primary function of a test light?

The primary function of a test light is to detect direct current (DC) voltage. A test light is a simple tool designed to indicate the presence of voltage within an electrical circuit. When connected to a circuit, the test light will illuminate if there is sufficient voltage to light the bulb, thereby confirming the presence of DC voltage. This tool is widely used in automotive and small engine diagnostics, allowing technicians to quickly check for electrical issues, ensuring that circuits are live and functioning properly.

Other options reference functions that are not the primary purpose of a test light. While measuring voltage levels in AC circuits, measuring resistance, and providing a constant power supply are essential in electrical diagnostics, these tasks are typically performed using different specialized tools such as multimeters for voltage and resistance measurements. A test light specifically focuses on indicating the presence of voltage rather than measuring it or supplying power.