this isnt helping nigel with his problem i only said it was worth checking the altenator as it can POSSIBLY cause a switch off problem.
right on said OLDER vauxhall that would not turn off if the ignition circit is back fed from the warning lamp there is just enough current there within the circit to hold the stop valve from closing.
i know what i found at the point of fault and i know that changing the altenator DID rectify the fault