Furuno 1622 Wiring Connection

[bcboomer]

I'm redoing a lot of old wiring and wonder about the shielding on the 1622 radar. The power supply cable has a 3 pin connector at the display so I assume 1 is for the shield wire.
The installation manual says to ground the display (wing nut on back) to a bolt welded to the hull. Won't do much good on a fibreglass hull.

What should I do with the shield wire?

Should I ground the display to the water?

My thru hulls are Trudesign so no ground to water there, maybe raw water strainer?