Immobiliser question.

[Dutch Scooby lover]

After the demise of my engine, and the following engine build I have also binned my standard Dash binnacle for a Stackash. I have since mounted the engine, and the dash,but have now run into aproblem, which we believe is the factory immobiliser. Car cranks, but does not fire. We are getting no spark. Fitted a battery from a mates car, as the stock one died on us after a lot of cranking Funny thing is the car has started once with the Stack dash fitted, but shut off after 5 seconds (this leads me to believe that it's the Immobiliser) Only thing different is the fact the stock cluster is gone,and also the factory warning light.Is this LED actually part of the circuit, or just an indicator. Also, how could I bypass it, if the light is actually part of the cluster. Car is a my98 Turbo, with built engine and PowerFC fitted. Also one more question, the stock watertemp sensor, could that be the culprit in any way,as I had to make a hybrid 1 sensor version, to be able to fit the Stacks Watertemp sensor. Normally the my98 has 2 sensors, one for the gauge/ECU and another one for the fans to turn on.I fitted a 2 into 1 sensor from a later model.FWIW the Stack and PowerFC both show the same temperature. In hindsight it would have been better to fit the Stack when the engine was verified as running, but that would have been a waste of time at that moment. Thanks in advance.