Good question! Has me wondering is it AC or DC powered? Most likely DC powered. Mine works fine but have not tried turning off various DC switches or AC switches to see if it goes through one of those. I do not have the wiring diagram with me, but I wonder if it shows anything. Following this thread for possible future need.
Heard from Grady this morning and they said they didn’t have any wiring diagrams for the CO2 for my year boat. Said to just switch to the new battery operated ones the industry has switched to. Bummer - I bought the hard wire one and lost the package to return it. Ugh!
Should not be too hard to run a new wire from the back of the electronics panel to that spot and install an in-line fuse. Mine is located in the entrance to the aft cabin, 07 330.
Maybe you should be looking for the CO wiring instead of the CO2 wiring
Typically a fuse will be near the power source... but maybe it's behind the monitor? In other boats, it's sometimes connected to a fuse panel behind a dash or sometimes on a breaker panel.