Yes, pin 3 receives battery voltage (positive) when the transmission is shifted to reverse. It is tied to the same circuit at the backup lamps.
There will be two "cutouts" on one long edge (one cutout on each end) and a locking tab for the connector lock in the middle. With the cutouts and tab on the top, looking at the mirror connection, pin 1 will be the pin on the right.
If you want more clarification, send me a private message with an e-mail address for you that can accept PDF attachments, as well as a quick "memory jog" of what info you are requesting, and I'll e-mail you the wiring diagram and connector face diagram.
-Rod