Originally Posted by
stevieturbo
I will repeat again.
The earth for the fuel pump WILL NOT go to the ecu. Never ever. It will go to chassis/battery ground. It may go to ground via the inertia switch ( I can't recall if the switch kills ground or the 12v supply ), but that's irrelevant here.
If someone has wired it to the ecu, it is incredibly stupid and no wonder it will cause problems.
It is crystal clear on the wiring diagram I have here ( LHD 3 door ) that the ground wire from pump is brown, and is to same earth point as fuel sender unit also earths to the body. Diagram says close to the tailgate lock.
There is no mention of an inertia switch on this one, but I know some lesser EFI Ford's did still use an inertia. Not sure on a Cosworth
12v from relay is black/red
i will re earth that brown wire thats in the loom next the fuel pump live it does have continuity with the chassis so it is earthed somewhere. on your wiring diagram does it show what relay or fused live is for the ecu mine doesnt. theres nothing more that i can do now. i would of thought the fused live would have blown to the ecu not unless some twat has put a nail across it. i did read on a post somewhere that your better of disconnecting the ecu plug before doing any welding which i recently did a month before the melt down and i carried welding just before the first melt down two years ago. but i allways remove both terminals from the battery and put my anti surge protector bridging the terminals which is pointless really as it may need 12v to make the devise work or show that its illuminating the green l e d confirming protection. maybe worth doing this in the future