[prkaye]

The dynon harness comes with three extra ground wires (pins 5, 16 and 17) that are available for extra sensors that require ground.
I'm using one of these for the Fuel pressure sensor, but I don't think I'll need the other two. Am I correct that these can just be left un-terminated, since the corresponding pins should be already grounded internally?

 

[flickroll]

You are correct. If you don't need them you can cut them off or leave them in the bundle. I'd put a piece of heat shrink on the bare end though.