1978 Merc black max 150hp will start but not shut down

[m.qualls89]

Hi I have a problem here. I had my transom replaced (long ridiculous story) but nowI'm left with their mess. I got the boat back and after tightening all the commections they had loose the boat will start and run just fine. But I can't kill it with the key. The gauges and what not turn off but I have to choke the motor to kill it. Any suggestions? also it is not in a runaway idle situation I can run it all day if I want to just cant kill it without choking it.

 

[DamianJP]

Re: 1978 Merc black max 150hp will start but not shut down

The magneto wire isnt getting ground out. Was the Ignition key replaced or removed when taken off the boat?

Should be a Black/Yellow wire, Black wire with a Yellow stripe.

Should be 2 posts on the ignition for the key, both labeled "Mag".

1 post has a ground wire.

1 post has the Black/Yellow wire.

Now when you turn your key to "Off" position, it grounds out the Mag and turn off the ignition system. Spark plugs will not spark. In your case they will not *Stop* sparking, hence the boat wont turn off.

Now it might not be the ignition key area, but you can get into that area and check to see. With motor running you can touch a ground to the post and/or the Black/Yellow wire that is on the ignition. If it turns off the ignition is wired wrong like I said. Now if it doesn't turn off then there a wiring problem on the motor side and we will have to do some "Hunting".

DamianJP

 

[m.qualls89]

Re: 1978 Merc black max 150hp will start but not shut down

Hey thatnks alot! It was actually an orange wire but you got me to looking in the right direction. Runs great and shuts off now lol. They had the wire off in no mans land but now its where it should be. Lesson learned if you want it done right do it yourself lol.

 

[DamianJP]

Re: 1978 Merc black max 150hp will start but not shut down

Wow orange huh?
Whats you serial number?

Sorry I hate giving the wrong info although it is RARE I do have a brainfart from time to time, does it look original or do you think they(Or someone in the past) changed it to orange?

Either way you are "Rock and Roll" and that makes me happy.

EDIT EDIT EDIT:
Now that im looking threw the manual , it might be original orange. Sorry again , Ill think/double check twice before I tell someone to ground out a color wire.

DamianJP

 

[m.qualls89]

Re: 1978 Merc black max 150hp will start but not shut down

Its ok you got me in the right direction anyway... Good thing i can use a voltage meter lol.

 

[Chris1956]

Re: 1978 Merc black max 150hp will start but not shut down

Orange was the old wiring color for the ign killer. I would have thought that motor would have had the new wiring colors because they changed over the V6's first.

BTW the ign system is not magneto. It is Alternator Driven Ign. Basically a CDI ign, powered by the stator and magnets in the flywheel. A true magneto is simply an ign coil, a set of points and a condenser,next to a spinning flywheel magnet.

 

[DamianJP]

Re: 1978 Merc black max 150hp will start but not shut down

Thanks for the info Chris. I always see the "MAG" on most if not all the ignition posts when I wire em' so it puts me in a bad habit of saying it.