Barney Guiton

This is all really useful for new boaters, cheers everyone! "3. If they are as you suggest (1 leisure and 1 engine) chances are that whilst the -ve terminals will be connected together by thick cable, the +ve terminals will not be connected together, but have separate wires leading away to the master switches. If both +ves, and both -ves are each connected together, the batteries are acting as one bank." Why are the starter and leisure negatives connected together? Trying to get my head around this very complicated circuit diagram. Thanks!