Engine wont turn off

[Y-O]

1986 Mercruiser 470 I/O. Boat ran fine the last 2 days. This morning went through a few key on/off cycles while drift fishing w/o a hitch. Then after starting engine, starter remained cranking as if the key was held in the crank position. After 30 seconds or so, the noise from the flywheel and starter pinion slowly went away, as if the plunger retracted. Engine running but will not turn off.
Disconnected ignition switch completely and engine will continue to run. Finally killed the motor using the shift interrupt switch.
Just looking for some input on where to start. Thanks all.

 

[Bondo]

Re: Engine wont turn off

Ayuh,.....

1 of the Starter Solenoids is Fried/ Welded in the closed position......

 

[Don S]

Re: Engine wont turn off

After 30 seconds or so, the noise from the flywheel and starter pinion slowly went away, as if the plunger retracted

Or the starter destroyed itself from the excess rpm.
Sounds like the solenoid stuck engaged which also puts power to the ignition while cranking.

 

[Coors]

Re: Engine wont turn off

And if you spin a starter fast enough, it becomes a generator, frying some other delicate parts in the electrical system, so make sure the charging system is ok before splashing again.