Applications: Can be used to test continuity, test the polarity of a voltage, check lamp, check electric motor, follow and locate short circuits, test for bad ground contacts and measure dc voltage from 2V to 24V etc. Powered by the vehicle battery directly. The illumination function enables automotive technician to test the electrical system in the darkness. Safety insurance. When the current exceeds 8A, the unit will disconnect the current automatically. Take the insufficient light environment in consider, the tool built in flashlight to indicate the DC voltage measurement. Do not use the unit around gas,vapor, or dust.When the rock switch is pressed(or rocked), battery current is conducted directly to the tip which may cause sparks when contacting ground or certain circuits.