if the voltage is really going that high there must not be any overvoltage protection or crowbar installed . if anything is wrong with the stator the voltage wont be high . the regulator is pretty much the only thing that can fail and cause the overvoltage . if the alternator switch wont turn off the alternator its either a switch or a relay thats no good . first things first , you have to figure out how your ship is wired since your not the builder . good luck