Inboard will not stop running once key was turned off and removed.

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Marc L

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Joined
Jan 2, 2007
Posts
2,368
Location
New Brunswick, Canada
This weekend, I helped my friend replace his alternator on his 4.3 Merc Alpha One.  So we tested it after to make sure it would charge and it did.  So I tried to turn off the engine by turning the key off and it kept running.  Tried a few times from the on and off position with no luck.  So we scratched our heads for a bit, then we disconnected the battery as a test, but since the new alternator works, that did not do anything.


So after more head scratching, I disconnected the wire between the coil and distributor and that stopped it.  Later found another connector that provides power to the coil, so we started it again and was able to disconnect it by disconnecting that wire.  I preferred that since I got a small shock when I disconnected the cable from the coil to the distributor.


Once we had a safe way to stop the motor, we then went for a 1.5 hour boat ride and stopped at a marina/restaurant for gas and food.  After we fueled up, we went to move the boat to another berth, but it would not start.  The attendant said it was fine where it was, so we went to eat.


After lunch, we tried to start it again with the key, with the intention to short the starter solenoid if that failed.  1st attempt with the key failed.  2nd attempt turned the motor a for half a second, 3rd attempt nothing, 4th attempt it started.  Once we got back home, we still had to disconnect the coil to stop the engine.


I'm wondering if it's a faulty switch stuck in the ON position and a faulty START position.  Although, earlier in the day, we tried disconnecting the ignition switch to stop it and it failed.


He's likely going to bring it up to a repair shop.  I'm normally not bad at figuring out electrical problems, but without a wiring diagram and where relays are located, I'm at a loss.
 
That's what my friend was inclined to do, only thing odd though is that we disconnected all 4 wires from the switch, and the motor kept running. 

By the shape and size of the switch, it does not look like an expensive component, it's pretty basic compared to a car's ignition switch.
 
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