[Freezebear]

Motor is a 89 mariner 150HP 6cyl. Sometimes the motor will start right up and will run OK. Sometimes you go to start it and it will not crank. When it does this there is no fire at any spark plugs. Motor does not run rough and has not died while running ever. have checked and rechecked my wiring. It only does this now and then, but is now more frequent. Am scared to take it out for fear it will die and leave me stranded. Any ideas of what could be causing this?

[dakk1]

Maybe your mercury switch is going bad. Sounds like something in the kill circuit.Dave..

[Freezebear]

What is a mercury switch?

[andy6374]

The merc switch is what kills the ignition when you turn the key switch to the off position. If you follow the black/yellow wires from your switchboxes it will lead to the merc switch.-Good luckandy

[Clams Canino]

"will not crank" = starter mtor will not crank the engine over = engine does not spin.Did you mean "will not crank" or "will not start and run" ?-W

[Freezebear]

I'm sorry I wasn't clear. It will turn over, but will not start. No fire at all from the plugs. I am still at a loss as to what exactly the merc switch is. Does it really have mercury in it and that's how the motor got it's name?