To clear up any confusion for those seemingly in the unkowns over the Can Area Network!
OBD11 or EOBD port as europe like to call it, standard is defined by ISO 15031-3 “x”, which was based on the US standard SAE J1962 and sets out the standard for the OBD connector.
OBD port 16 Pin connector:
Pin 4 – Chasis ground
Pin 5 – Signal ground (Depending on the vehicle signal ground could be connected to chasis ground through a “Y” connector. Whats inportant is this pin could have a resistor or nF cap between the pin and chasis ground, so Pin 5 should not be used as a ground)!
Pin 16 – Battery Power (Type A 12v) (Type B 24v)…
5.3.9 Pin 16 (vehicle connector terminal) is designated Unswitched Vehicle Battery Positive and must be implemented in the vehicle connector. This terminal must be connected directly to the DC Positive of the vehicle’s battery. This connection does not preclude the use of a fuse or other circuit protection elements. This circuit may be grouped with other similar circuits,(i.e clock memory) and must be able to supply a minimum of 4A.
5.4 5.4 Vehicle Connector Terminal Protection — It is recommended that the vehicle manufacturer provide circuit protection in the event that the terminals of the vehicle connector are shorted together.
So unless any would like to argue the point – Pin 16 is battery positve (linked directly to the vehicles 12v battery) for the purpose of powering external equipment, primarily OBD diagnostics equipment and as since had uses from powering Gateways for EV drivers, dataloggers, tuning, powering external devices etc and emergeny vehicles carnation ECU (yes one of my many jobs). More importantly, the vehicles controllers are on CAN network, which does not intergrate with pin 16.
So except for the fact that you could drain the 12v battery, connecting a dash cam to the ODB II port should not give any problems. “However, as in my initial comment, it is recommended a switch or timed switch be used to prevent the 12v battery from draining and that a fuse is incorparated in line with the dashcam specifications.