If you look at the plug with the ground pin (the large round one) facing downward, the flat pin above and to the right is the common wire (not the same as ground) and the one on the left is the hot wire.
In a plug without a ground pin, modern electrical code states that a 2 pin plug will be polarized. If you look at a modern 3 pin wall outlet, the circular hole is for a ground pin. The left flat pin (common wire) is larger than the right flat pin (hot wire). A two pin plug is supposed to go in only one way.
Dug one out.
Probes from my DMM won't fit
Used a magnifying glass to help my old eye's, there's a + and a - etched into the connector
+ = bottom left on your little diagram
- = top/center
That would leave the bottom right as the communications pin.
No guarantee's whatsoever
wow thanks man, i probably would have guessed wrong. Now about your reference to my rudimentary diagram, vis-a-vis left/right; are you considering said diagram to be a representation of the pins on the laptop or the holes in the plugwhich will receive the pins? thanks again...