Hi Aidan,

that's fair enough actually, you are right with chicken and egg, but when the car doesn't start there is no earth for the fuel pump relay from ECU as well, not just when it cuts out.
I wonder what exactly would you be testing with a scope to tell if it is a cause or an effect? I don't think a scope would show much more on this earth wire, so I wonder what you have in mind that you would test?

Thank you very much for your help.

Best regards,

Dominic