I was helping a friend with his boat Friday. After the motor started the starter would continue to run once the key was returned to the run position. He could make the starter quit running with a quick whack on the solenoid (it's separate from the starter). That's easy I said, bad solenoid. After replacing it, the new one did the same thing. So did the next new one. New starter, same result. Any ideas?

Solenoid on the top of the motor. Depending on the engine, it is under the 50 amp breaker, or near it