Puma starting problem

Hi Folks
I'm trying to get a good friends defender started, It turns over and promptly starts, runs for about
1/2 seconds maybe less, any ideas please, all I have done is wiggle the relays so far
they did have the barrel changed with a new key, the new key fits the ignition and old key opens the door
I have no remote and guessing an immobilizer problem any help much appreciated

If it runs, even briefly, it is not immobilised. Which is odd if you have no remote as that is needed to disarm the immobiliser. The immobiliser must have been disabled. Get a diagnostics tool plugged in and get the fault codes as a starting point to finding what is wrong.