Relay-switched output doesn't work

[gardners]

When the driving GPIO line toggles, the N-FET doesn't seem to switch on, to allow the relay to switch.

It looks like the N-FET may not be wired correctly.
It has three pins: two on one side, and one on the other side.
I don't know exactly which component is used as the N-FET, but assuming it has the same pinout as: http://www.nxp.com/documents/data_sheet/BF862.pdf, then the gate voltage is connected to the drain pin, instead of the gate pin. This would go a long way to explaining why relay never switches.

What we have probed on the PCB, suggests:

         +--+
         |  +- RSIG
    GND -+  |
         |  +- Relay coil (with +5V pull-up resister)
         +--+

What we think it should be is:

          +--+
          |  +- Relay coil (with +5V pull-up resister)
    RSIG -+  |
          |  +- GND
          +--+

But different N-FETs have different pinouts (e.g., http://www.nxp.com/documents/data_sheet/BSH105.pdf), so we really need to test what is going on.