Self-Powered Test Lamp

Self-Powered Test Lamp:

Use a self-powered test lamp (J 21008-A or equivalent) to check for continuity. This tool is made up of a lamp bulb, battery and two leads. If the leads are touched together, the bulb will light.

A self-powered test lamp is used only on an unpowered circuit. First disconnect the vehicle's battery, or remove the fuse which feeds the circuit you're working on. Select two specific points along the circuit through which there should be continuity. Connect one lead of the self-powered test lamp to each point. If there is continuity, the test lamp's circuit will be completed and the bulb will light.

Never use a self-powered test lamp on circuits that contain solid state components, since damage to these components may result.