Note: These meters are stepper motors and need to be powered on to return to zero. It is normal that the pointer does not return to zero.52mm Air Fuel Ratio Gauge 7 Color backlight + Narrowband O2 Oxygen Sensor Car Gauge Fit for 12V Car Air Fuel Ratio AFR SensorFeature:- High Precision - Racing look enhance the characteristic to your car/vehicle - Fitment : Universal 52mm diameter Voltmeter fit for Motorcycle Car /Truck/ Gasoline Engine (The compatibility just for reference .Please make sure the item fit for your car before purchase.)Application:Color:Black Voltage:DC 12V Diameter:52mm/2 Material:Plastic Quantity: 1 SetPackage Included: as the picture shows1x Air Fuel Ratio Gauge OR 1x Sensor OR 1x Gauge CupNote: The gauge cup needs to be purchased separately, the gauge does not contain the gauge cup Wholesale and drop shipping are both welcomedFor wholesale, we will offer the discount or free express shipping which only takes 3-7 days to arrive. For drop shipping, We could send the goods to your customers directly and won t leave information about us if youd like to.O2 sensor instructions- The white line is at heater ab - Black line signal line C, gray line signal ground D - The green wire of the instrument is connected with the black wire of the sensor. - The gray line is connected to the negative pole of the battery. - One white wire connect with the car shell or battery negative pole. Another white wire connect to the ACC line of ignition switch - The white line is the heater and does not distinguish between positive and negative electrodes - About the air fuel gauge, please see the installation instructions