Mate new 360 Immobilzier

I have just purchased a new immobilizer and 3 keys. Does anyone know the process to mate the new immobilizer ? The 2 immobilizer boxes I got seem to be plug and play, I have now swapped them over, tried to start the car and nothing. I then read that the immobilizer is mated to the right engine ecu, so you can swap the left and right engine ecu over in the hope that the left one is a virgin. I have also done this but car will still not fire up. Is there something else I am missing ?