I think this is the same as the US 20MT. The top batteries are wired in series to make 12 volts, and the bottom are wired in series to make 12 volts. Hope you have at least the boots on the long battery cables to show you what is posotive and negative.

There is a short cable between the top and bottom batteries. Truck has four 6 volt batteries. this is not too detailed. I hope it is enough to figure it out.