YueYueZou&reg; Automotive Relay Tester Diagnostic Tools for Battery, Car, Electric Components with LED Tests three of the most popular relay types. Tester controls the tested relay for proper opening & closing. Tester uses 12V power from car battery. Quick and easy off the car relay test. Light RED LED if the relay tested is abnormal, if not light GREEN LED. Attention! The car battery must be 12V battery, and the voltage of the battery is among 11V--15V. Ideal for coil resistance above 20 ohms.