The problem has been solved, indeed it was a disconnected wire from the ignition coil. Might have become loose while we took the engine out to replace all gaskets.
However to provide a solution to future viewers, let me share some more information. My car is a 1976 RHD 260Z with a L20 ET engine. I came to the above solution after reading page 61 of the EFI bible. Yes Pin #1 on the ECU connects directly to the negative terminal of the ignition coil.