Mercury 50 hp won't turn off

[james42]

I have a 1981 50 HP 2-stroke Mercury which will not stop running when I turn the key off. The starter was replaced recently, and the first time I tested it to see if it would crank before getting to the lake, it continued to run when the key is turned off. Any ideas?

 

[alldodge]

Howdy

A 4 stroke motor needs a connection made to run and remove the connection and it dies. The 2 stroke is the opposite, it needs a ground applied to the magneto to stop and removed to run. In the pic below there are 2 "M" terminals. One of the M is grounded and the other goes to the Magneto. In the OFF position there is a connection across the 2 M terminals which grounds the Magneto. This same thing is used for the man overboard kill switch