Thanks fellas for the time and effort spent steering me the right way. Yesterday, by phone, the dealer tried walking us step by step through the circuits and I was getting more and more confused. All three clutches were down in voltage, looked like it could be the seat safety interlock, so decided to get a serviceman out today. Turned out, as Dan mentioned, at every joint, fuseholder, brushcarrier, etc there were small voltage drops, nothing major in one particular spot. So he put a relay in for each clutch which bought them all up above 10.5v with engine off and I guess up another 1.3v which the batteries came up with engine running. So with a bit of luck we will be into the wheat in the next couple of days. Cheers.