Answering your question: Using the diagram on the .pdf file (see my previously message), attach the white cable (the one named "Hi low ign" to the second borne on the fuse box (counting from down to up, left side of the fuse box). The yellow one goes directly to the (+) borne on the battery (please, don't forget the fuses, on this setup are mandatory as a safety measure). Remember disconnect the battery before make any procedure. Add some additional spare fuses to your tool box (you would be need it on the road in some far future).

Of course, the gauge (diameter) of the cables are important, please follow the suggestions already send for other fellow volvofans on this thread.

Joaquin