Engine won’t start after engine swap

Hi all
ive just swapped a M15a into my 2006 Jimny 
ive just tried to start it and nothing happens 
there are a few clicks that I can hear but the starter motor isn’t spinning 
Any advice?
i was wondering if the immobiliser might be a problem 
ive tried both keys
thanks for any input 
Tom

Just tried one of the keys again
Locked and unlocked the car a couple of times
It now starts and runs for a few seconds and then cuts out
Could this be the immobiliser?
Engine sounds sweet which is a bonus!
Tom

Now back to clicks and no starter!!

Could be a bad earth to the motor or a loose starter wire?

I’ve cleaned up the starter motor connection and it fires up now but only runs for 2-3 secs before cutting out again

First, the immobilizer won't prevent the starter from engaging and cranking the motor, that's going to be purely an electrical issue, and second, it's extremely unlikely that the immobilizer will allow it to start and then shut it down after 2~3 seconds.

Look at the dash lights, the immobilizer warning light is most likely an orange padlock, newer models might have blue & red keys, an immobilizer fault will usually show up as the starter cranking the engine over without it firing and the warning light on the dash flashing.

It'll behave like a no fuel/no spark failure because that is exactly what it is, the immobilizer shuts down the EFI system.

Start by testing for no fuel - spray starting fluid into the intake whilst cranking the engine, if it starts & runs for as long as you're spraying the fluid you have a fuel delivery issue, you can also check for a spark at the plugs.

Good old fashioned petrol engine troubleshooting techniques.

I'm going to stick my neck out, you have a fuel system blockage causing the pressure to drop below what's required to lift the injector pintles off the seat, there is enough flow to build pressure into a "deadhead" situation, but as soon as the injectors open, the pressure drops too low to sustain injection and the engine dies.

If it starts & runs on starter fluid, get a fuel pressure tester and verify the pressure.