No Oil flow alarm not working

[Reg Sch]

I have a 1989 110 hp johno on which the VRO unit appeared to fail (no oil flow alarm activated) I purchased a new OMS kit as the original pump was superceded a later model was supplied . the difference was the electrics original installation was a 3 wire unit and the new one a 4 wire. All the necessary part and instructions were with the kit to convert to 4 wire.
Installation went well, how ever when running the motor with oil supply disconnected, as instructed, to test the "no oil flow alarm" the alarm is not activated.
The alarm chirps when the ignition is turned on, and works if the overheat wire is shorted to earth so I believe the alarm is ok.
Help?
Reg Sch

[boats.net]

It should activate but will take some time after disconnecting supply hose. Make sure you are on running engine on premix gas/oil while testing oil system.

[Reg Sch]

It should activate but will take some time after disconnecting supply hose. Make sure you are on running engine on premix gas/oil while testing oil system.

The unit was installed as supplied, ie straight from the box, and had never been connected to the oil supply. It was run several times on premix, at least for 5-6 minutes in total. No alarm.It seems the new unit may be faulty, is there a check I can carry out to prove its function.
Appreciate any help, as my boat is a 7 hour round trip from my home.
Reg Sch