Re: Ignition problem, stumped!
Take any shop manual, for any car or gasoline boat. Check out the pages on diagnosing a starter problem, they're all pretty much the same.
When you hit the key and nothing happens, that usually means you are not getting power to the starter solenoid. If there's no "kerchunk" or "klunk" from the starter, there is no power getting to the starter solenoid. That usually means a loose or corroded wire, and you need to just run hands and eyes along the wiring to find that.
Yes, it could also be the ignition switch but again...any shop manual will give you the list of thing to check, in sequence. There's nothing that should be unique to the A4, or to a boat versus a car, for this one.