Hi all - thanks for all the help so far. I've done so many diagnoses on her I feel like I'm in an episode of House...
The latest battery of tests reveal:
Battery voltage when cranking drops to 10.6V (from 12.9ish), so that sounds OK if 9V is what you need to kick the ECU into action.
Removed the fuel hose and turned the ignition on. I got a dribble of fuel from what was already in the fuel line, but no spurts of fuel from the pump, suggesting to me the fuel pump isn't being properly primed (backed up by no sound when the ignition is turned on).
Checked the voltage across the FIA switch - reads 12.9 when switched off, 0 when on, which to me says it is working OK.
Have checked and tightened as many earths as I could find both little and large (two by the ECU, all the fat ones under the bonnet, a couple under the scuttle on either side, the fuel tank to chassis one) and still no joy
The one interesting thing I did find was when checking the voltages to the fuel pump. When the ignition is on, there only appears to be just under 5V going to the fuel pump. I can't quite understand this - I am assuming I need 12V to kick it into life.
I am basing this on the voltage differences between the four wires going to the fuel pump. The four are:
YG168 - which appears to be the earth - runs to the inertia cut off switch
GB168 - which appears to be the live
SG196
B10
The difference between SG196 and GB168 is just under 5V, and the difference between B10 and GB168 is also just under 5V. YB168 to all the others is 0.
Does this shed any more light, and any ideas where 7V is being lost?
Thanks,
Simon