Here are the monitor voltages for my FTS 4100 several days after lock.
| DB25S pin | Voltage* | Description* |
| 1 | 0.00 | |
| 2 | 0.00 | |
| 3 | 0.00 | |
| 4 | 4.42 | Synthesizer lock |
| 5 | 2.13 | Electron multiplier |
| 6 | 3.35 | Ionizer |
| 7 | 3.53 | Quartz oven power |
| 8 | 0.63 | Cesium oven |
| 9 | 2.87 | Beam current |
| 10 | 3.56 | C-field current |
| 11 | 3.46 | Control voltage |
| 12 | 0.00 | Ion pump |
| 13 | 0.00 | |
| 14 | 6.99 | C-field reference (7V) |
| 15 | 3.18 | C-field adjustment |
| 16 | 0.00 | |
| 17 | 5.00 | Alarm reset |
| 18 | 0.00 | |
| 19 | -31.92 | Relay |
| 20 | 0.00 | |
| 21 | 0.00 | |
| 22 | 0.00 | |
| 23 | 0.00 | |
| 24 | 0.00 | |
| 25 | 0.00 |
* Voltages referenced to case ground.
* Pin descriptions have not been verified on this unit.