Hi
Mine is exactly the same.
Mine will start eventually and be ok for the rest of the day but I will get same issue in the morning.
The clicking you get comes from the relay which trips out.
I think this is down too not having enough power to heat the plugs.
Something is dragging the battery down like a bad earth somewhere.
It might be worth checking how much power your battery has when the ignition is on.
You could always bypass the relay and have a switch in the cab to heat the plugs.
Hope this helps
Steve, March 2009