Between the terminals in series (see your H.A. Manual for resistor size) CT-6 PROBE AND WIRE CHECK-OUT It is advisable to check the sensor probe assembly before and after installation in the earth. Use a good multimeter. With the probe wire disconnected from the control unit, measure the resistance between the RED and BLACK leads. Bluetooth car kit User manual details for FCC ID VTTCT made by Cartel Mobile Solutions Inc. Document Includes User Manual User manual.