[Sparks]

No bell at all Dave.

I've just finished wiring as per Pell's instructions and diagram and I'm still no further forward. With this jack unit, the problems start as soon as the hook switch wiring comes in, i.e. reduced sidetone volume and failure of switch to kill the line when pressed. As of now, the unit is back in its original configuration with a standalone handset plugged in. It works fine without any switches. Mystery !