1. Through the continuous automobile battery to the relay coil, the detector can properly check the relay contact function. 2. The tester observes contact data, closure time, relay inertia at each test stage, etc. 3. Test to properly control the opening and closing of the relay. 4. If the relay is abnormal the red LED light, it's normal the green LED light. 5. Fine workmanship and good performance. 6. Easy to operate. 7. Convenient to carry. 8. in use. Most car lights, wipers, , air conditioners, electric seats, electric doors and , anti-lock brakes, and audio all use relays. Automotive relays suffer from vibration, high temperature, low temperature, humidity, etc., which reduce their life. But once the relay fails, it immediately cause the paralysis of the system components, and even cause the entire vehicle to be unusable. Therefore, it is very important to regularly check the relays inside the car. Tester check for proper functioning of the relay contacts by connecting the car battery (11V--15V) to the relay coil. Colour:Black & Red Material:plastic Package Contents: 1 * Car Relay Tester Only the above package content, other products are not included. Note: Light reflection and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.