I was just able to make a network cable by splicing together a blue network cable with one connector missing and a black pigtail with gray connector (fluxgate cable for AD10 on the heading sensor).
I will note that the shielding in the black/gray combo cable is quite different (much more robust) than the blue network cables. Since the black with gray connector cable is used for AD10 heading sensors which seem to be quite sensitive, you might run into interference issues if you use the blue cable for the majority of the cable run. I actually just picked up a 10m fluxgate cable on ebay for $50. Might be worth a purchase, especially if the cable run is difficult to do in your boat, like it is in mine. Redoing it after finding out you're getting interference is not ideal.