They are both correct.
The pin sockets that are used in diagnoses depend on the vehicle.
My diagram just happened to mention #3 cuz it was for a 190E.
#1 is usually ground, but the other depends on which code system the car uses.
So the tool can be used not only on all pulse code cars, but also the different systems of each car .
[ in other words, the different pins - i.e.- emmisions pin, ABS pin, A/C pin, etc.
The other advantage to having this tool is it is also used to erase a codes.......