Every time it has happened to me its been the bilge switch,, any exposed wire that is "hot" and gets wet can do it..
When you sink your ski in salt water just reaching in the water in the hull the battery will light your eyes up !
A long time ago I always used cheap toggle switches and man, one time in Ventura I couldnt even hold onto the bars, touch the ski anywhere/anytime.. I had to knock the wire off with a stick !