HELP with immobiliser issues

Hi Guys,

i am in need of some urgent help, i am part way through a project puma 1.7 petrol,

i have stripped the insides including all central locking and unrequired electrics, I have also swapped the engine for another 1.7 engine,

My issus is that i have connected a battery to car and the alarm goes off and doesnt turn off at all,

i have tried starting the car to see if this helps, but nothing happens apart from all the dash lights flashing and all the needles going crazy,

ANY IDEAS?

Is the battery fully charged?

Changed anything to do with the ECU / Alarm / Immobiliser?

Battery is brand new.not changed anything to do with ecu/alarm or immoboliser to my knowledge.everything else is strpped out though