When the probes touch the terminals while the car is off and the battery is resting, the multimeter display should show a reading of 12.2 to 12.6 volts
Good day. Thank you for your question.
For the external voltage, the AVL ID is 66. For more information, please refer here - https://wiki.teltonika-gps.com/view/FMB920_Teltonika_Data_Sending_Parameters_ID