Pete,
Now this is not somethiing I have done,(as usual!)
Have you got a multimeter? If so you need to find out if the 'sensors' warning contacts are closed, as I suspect they will be, before you fit it. If they are closed the sensor will have to be fitted to the port that the low pressure switch is fitted to, if you still want the buzzer of doom to work as well.
As I have said before I believe that the actual oil pressure is the same at both ports, only the switches vary, both in the pressure at which they operate,
and the sense in which they operate. The high pressure switch contacts are normally open with no (or low) oil pressure, the low pressure switch contacts are closed with no (or low) oil pressure.
If you fit the sensor in the high pressure port, you will probably find the buzzer of doom will be on continuously above 2000 rpm. Assuming you reconnect the wiring to the sensor. (alternative earth the buzzer of doom wiring and forget it.)
A lamp and battery will also confirm sensor contacts open or closed.
Regarding the other wiring + battery plus via a low rated fuse and - a good earth connection would be my guess,
If anyone knows for sure please help
Now I am wondering if there is a low pressure oil light incorporated in the instrument itself. Hows that going to affect the game plan. One thing it cannot be any worse than that of the England world cup side

You may need on site help Pete!
Mike