12V pos-neg + Shield?

[TimC2520]

I'm hooking up a NMEA 2k starter kit to a Blue Seas blade fuse block.
+ to POS, - to NEG. What about the shield? A totally separate ground BUS?
:?:

 

[sparky]

If you have a dedicated sea ground, that'd be where the shield goes. Otherwise, I've attached it to the battery ground without issue in the past.