Problem with fuel pump

[Bax]

My car suddently cannot start.
It cranks normally.
I realised that the fuel pump doesn't work when the key is in the on position.
The fuel pump has a 4 cable connector.which 2 should I check to see if there is voltage on it?
I think it's a wiring problem and not a pump failure because it just didn't start after a 5 minute stop.

[Bax]

Anybody with an idea?
I checked the connector of the fuel pump.
I get a 12v reading, a ground wire, a 6volt reading and a mystery wire (black if i remember).
how can I test the fuel pump outside the car?
I also bridged the F/P and Gnd pins on the diagnosis connector and the pump still doesn't start.
If I take the pump out, how can I see if it is working?
What triggers the pump to start working?

p.s. When I connect the fuel pump to the connector, the pin that has the 6V, goes to 2.78V.

I also checked the circuit opening relay and the resistances between the pinouts are in spec.

Any ideas?