pin out for checking error codes?

'93 s10 2.8L V6

i want to check the error codes and was told to cross the A and B ports under the steering column. no problem except the ports aren't labeled.
there's 6 in a row on top and 6 in a row on bottom. being used are what would be 2, 4, 5, 6 on top and 2, 6 on bottom.
how do i tell which is A and B??

thanks