How to connect a Ford Zetec 2.0 crank sensor ?

[Wgroove]

Hi everybody,
I'm preparing everything to connect my zetec to my Emerald ECU.
I'm having some doubts bout connecting the crank sensor.
The diagram from the Emerald says:
Sensor + Crank sensor or digital distributor input signal
Sensor - Earth return for main/cam trigger sensors

How can i find out wich is + and - on my sensor ?

Many Thanks !