the Onan 4000 in our old '92 Winnebago started by itself several times, always when wet. Even though the secondary switch in the range hood was nowhere near any water, disconnecting the wiring to that switch solved the problem.
Had the same problem in our houseboat after installing 2 new ignition switches on our flybridge. First night it rained, the starboard engine started itself up in the middle of the night, scared the bajezzus out of us, we thought someone had broke in! Wasn't long afterward the OTHER engine started itself too. Water and electric switches don't mix!
2000 40' Tiffin Allegro Bus \ 2002 Regal 2860 Commodore
1988 53 x 14 Skipperliner \ 1995 32' Party Cruiser
1984 Goldwing Aspencade \ 1976 Harley Sportster