Checks 6 and 12V circuits for voltage and checks spark plug for spark.Place probe in end with regular bulb to check low voltage. Checks headlights, taillights, turn signals and other circuits. Tests for faultysockets, connections and broken wires. Place probe in end with neonbulb to check for spark voltage. Tester comes in a shock-proof case.Includes 36” cable. Uses bulb #1893.