electrical problems preventing spark - I'm stumped

[mcurcio1989]

I have a 1981 80hp 4 cylinder mariner. The engine cranks over just fine but has no spark. The first thing I did was remove the Black / yellow wire off of the cdi unit and sure enough it cranks over, produces spark and fires right up. Then as soon as you touch the black / yellow wire to its post it shut off. I unplugged the controls and jumped the solenoid to eliminate any kind of wiring issue in the controls or there wiring harness. Still no spark. So I assumed it must be something to do with the "mercury tilt swich" I unhooked the black and yellow wire from that to isolate it from the system and that did not help.

Here is where it gets more confusing to me. It appears that the black ground wire that feeds the controls their ground is fastened on the cdi unit right net to the yellow and black post (but on the frame). I can remove that wire and it will run. So I got out the multimeter. I assumed that somewhere along the line the black and yellow wire is grounding to that black wire but it is not according to the ohm meter. Black yellow wire is not grounded unless the key is in the off position. However as soon as i put the black and yellow wire on its post on the cdi i get like 30m ohms and no spark. This defies all logic and I have no idea what is going on! Any ideas here?

 

[Chris1956]

Re: electrical problems preventing spark - I'm stumped

Well, the black/yellow wire is somehow shorting to ground. If you unplug the harness and it still kills the spark, it is obviously in the motor harness. Did this just start happening?

 

[CharlieB]

Re: electrical problems preventing spark - I'm stumped

Anytime you disconnect the black/yellow kill wire and then get spark you have proven that there is a short to ground somewhere.

Forget the black wire, use the motor block as your ground when testing.

Double check the lanyard switch, they do go bad, sometimes the clip wears enough it fails to fully move the plunger and what may look good, isn't.