If it is needed to connect any serial devices to the +3 it requires a serial lead with connections as follows:
___________________________
__| 6 5 4 3 2 1 |
|__ ### ### ### ### ### ### |
|___________________________|
RS232 socket
| PIN | FUNCTION |
| 1 | GND |
| 2 | TXD |
| 3 | RXD |
| 4 | DTR |
| 5 | CTS |
| 6 | +12V |