Mercruiser 3.0 constant crank?

[19723.0merccruiser]

I have a beach comer with a Merc cruiser 140 3.0 four-cylinder engine. Why when I turn the key to the on position does the motor crank. I’ve been tracing wires and cleaning up connections. Everything seems to be good. The last thing I’m at is the key might be faulty, any help would be greatly appreciated. First post on this form. Can’t wait to get this bad boy in the water.

 

[makomark]

The starter motor should NOT crank the engine over with the key in the RUN position...if it does (and I suspect you just got the boat) something is hosed up...could be the ignition switch but I'd be more incline to think somebody did some 'work' that wasn't correct...likely some wiring was not replaced correctly...but hard to say...do you have the engine serial number?

 

[19723.0merccruiser]

Yes, I got the boat for free. Person I got it from claimed it only needed a starter and new battery. Serial number is 487-3523.

 

[Bt Doctur]

remove the switch to see if:
B has a red wire on it
I has a purple wire on it
S has a yellow/red stripe on it

 

[19723.0merccruiser]

I replaced the ignition switch to fix the problem.

 

[19723.0merccruiser]

Now she just won’t stay running, time to tear down the carb

 

[jimn]

Now she just won’t stay running, time to tear down the carb

Have you checked for voltage on the purple wire when it's not running?