When connected to a Paging Station or VI-6, the VPSI-1 DB-9 connector is used to facilitate connections to LED indicators as follows.
| Pin Out | Function |
| Pin 1 | Busy LED |
| Pin 2 | Host TXD |
| Pin 3 | Host RXD |
| Pin 4 | Talk LED |
| Pin 5 | GND / 0V |
| Pin 6 | TXD Link Back |
| Pin 7 | RXD Link Back |
| Pin 8 | Wait LED |
| Pin 9 | 12 Volts |
When connected to a Paging Station, the DB-9 connector is used for VTP control from an external control system using RS-232 serial commands. See the PS VTP Interface section for the necessary 3rd party RS-232 serial connection settings.
| Pin Out | Function |
| Pin 2 | Receive Data (RxD) Input |
| Pin 3 | Transmit Data (TxD) Output |
| Pin 5 | GND / 0V |
| Do not wire any other pins | |
See the VPSI-1 Hardware Manual for more information.