Thank you for your response Brooksmyk, I am not worried about the main battery connections as they are obvious to me. However when I collected the C5 the seller wanted to demonstrate lights and did not seem to know which way to connect the battery. In fact he tried both ways so I fear the worst, perhaps being a battery in poor condition may have saved the electrics, but then what has he done over the years he has had it stored I wonder?
I have now found a copy of the wiring diagram and can at least check I have the correct connections to the control box etc. thanks.