There are two types of diagnostic link connectors (DLCs) defined by SAE J1962 - Type A and Type B, shown below. The main difference between the two connectors is in the shape of the alignment tab.
(courtesy of SAE)
|J1962 Vehicle Connector, Type A
||J1962 Vehicle Connector, Type B
OBD-II connector pinout
|2||SAE J1850 Bus +|
|7||ISO9141 K Line|
|10||SAE J1850 Bus -|
|16||Vehicle Battery Positive|
According to SAE J1962, Type A DLC "shall be located in the passenger or driver's compartment in the area bounded by the driver's end of the instrument panel to 300 mm (~1 ft) beyond the vehicle centerline, attached to the instrument panel and easy to access from the driver's seat. The preferred location is between the steering column and the vehicle centerline."
Type B DLC "shall be located in the passenger or driver's compartment in the area bounded by the driver's end of the instrument panel, including the outer side, and an imagined line 750 mm (~2.5 ft) beyond the vehicle centerline. It shall be attached to the instrument panel and easy to access from the driver's seat or from the Co-drivers seat or from the outside. The vehicle connector shall be mounted to facilitate mating and unmating."