What about a real solution?
There's three wires on that post, anyone know what they are? I'm guessing power, ground, data.
Get a regular boat key (I'm thinking one of those metal things like what goes in your car) with dual pole dual throw.
Put that across the data line and the power, then take the dess key and cut away some of the rubber, just enough to get a soldering iron in there...
Solder the two pins to the dess post, and leave the thing under the dash forever.
Anyone who's about to replace their key wanna give it a try? Mine works so I'm going to leave well enough alone for now.
Its a boat, not a PWC, so it doesn't need a kill switch like this.