All help has been very appreciated.

Tony's post in particular set me on the right track, as I immediately realised my error. Last night I knew the car would be up and running today - slept well!

Replaced engine relay and decided to replace pump relay as well. Customer didn't pay for my mistake .. he paid the correct price and I learnt a lot about how the system worked.

Nice to speak to you today, Mark.

Cheers All!