fuel flow sender harness- ground wires?

[Zimmerman]

I'm installing the speed/fuel managment gauge. I have one engine. The harness has two fuel flow sensor plugs, two black ground wires going into one terminal, and a colored wire. I'm pretty sure the colored wire (forget off the top of my head what colors it is) doesn't get used, I use one plug to my sensor. My next question is- do I need to ground the black wires?

[boats.net]

Grounds at gauge do need to hooked up.

[Zimmerman]

I figured that. I found an old thread that says the ground and white/pink wire at sender side is for the optional water alarm. Don't need that.

[Sequoiha]

I would also hook up all the grounds, even if you only have one motor and the gauge set up is for 2, hook up all the grounds.