TD5 defender immobilizer issue

Help desperately needed
I'm not getting any power to the starter
I have attempted to remove the after market thatcham immobiliser because the truck failed to start
I do have ignition lights and tank pump running, all ready to start but dead at starter.
I ran a direct live to the starter and she ran for three seconds only.
Any one got even a clue?
Would replacing the ECU solve this
I'm told that the immobiliser should not have anything to do with ECU.
Any help,I would be extremely grateful

Is it the factory immobiliser causing the problem, or starter relay.

Thanks
It's an aftermarket touch immobiliser
Il try and locate the relay, unless anyone knows which one it is?