[Lotus]

the stock ÉCU requires an immobiliser signal, except the PRC version.

 

[Lotus]

simple stuff: does the ECU activate at all? Do you get OBD signals from it?
Might be as simple as main relay activation not working.

 

[Lotus]

awesome.
It needs a big ground strap from the gearbox to the chassis and from chassis to battery to transfer the starter motor and alternator currents. Your car cranked, so it could not have missed that big ground strap.
Then there is the engine loom ground strap on the valve cover. And that is essentially it.

 

[Lotus]

could have been too small causing a sufficient voltage drop across the strap and therefore the two sections of “ground” to “divert” current supply from elsewhere in the loom blowing that fuse.