here is a look at the OBD-I readout plug under the dashboard on the rightside of the steering wheel:
I actually replaced this, after trying to move one of the pins over. The socket actually only has pins 1,2,3 connected on the right.
The apparent pin on the lower left is just bad lighting. no metal or wire there.
Here is the supposed pinout of this plug:
The 160 Baud connection is optional (and not found on the Lumina). I tried shorting A & B and did not get any flashing readouts.
Only A, B, and M are connected on this car.