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Dominick, Marine Mechanic
Category: Boat
Satisfied Customers: 1009
Experience:  25 Years Experience as Mechanic, 20 Yrs Boat Yard Owner/Mechanic, Factory Certified
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I've traced a ground fault to within my Yamaha 150 outboard.

Customer Question

I've traced a ground fault to within my Yamaha 150 outboard. But I can't figure out where the current crossover is occurring. If I disconnect the main black electrical harness in the engine, the fault remains. If I disconnect the hot wires at the solenoid, it disappears. The smaller of the two red wires connected to the solenoid creates a full 12V ground fault, but I can't trace where that red wire goes. Nothing visually obvious wrong.
Submitted: 2 years ago.
Category: Boat
Expert:  Jason replied 2 years ago.
Hello my name is ***** ***** am I speaking with?
I don't quite understand what it is you are doing. What problem is the engine having that you are trying to correct?
Customer: replied 2 years ago.
My name is Tom. Do you know what a ground fault is? I'm loosing current, through some unintended circuit. I've disconnected all the fuses to things like lights, horn, wash down pumps, bait aerator pump, radio, etc. So, none of the red (positive circuits) should be drawing current. When I attach a volt meter from the positive lead of the battery, to the (disconnected) positive wire that runs to the engine, I read 12 volts. It should read zero if nothing is drawing current, or completing the circuit (like I said, I've disconnected all other circuits).
Customer: replied 2 years ago.
Should I expect a reply, or are you done with this question?
Customer: replied 2 years ago.
(Posted by JustAnswer at customer's request) Hello. I would like to request the following Expert Service(s) from you: Live Phone Call. Let me know if you need more information, or send me the service offer(s) so we can proceed.
Expert:  Jason replied 2 years ago.
I don't quite understand, is the battery running dead on you when the engine sits, is that what is going on?
Customer: replied 2 years ago.
I haven't noticed it running down when it sits, but I always turn off my battery selector switch. When running the boat is running at idle speeds, I notice that the voltage being received at my chart plotter fluctuates between 10-11 volts, which sometimes causes it to shut off. And the horn won't work. If I rev the engine, the voltage will rise to 13, and the horn works. After a day on the water, the battery is run down. Using my voltmeter, I tested for a ground fault, and see that I have one. And that takes me back to my previous statement, of having disconnected all the power drawing circuits (including the bilge pump), and still see current flowing across the positive lead.
Expert:  Jason replied 2 years ago.
What does the voltage read at the battery terminals with the engine running in the 1500-2k rpm range?
Customer: replied 2 years ago.
Around 13.
Expert:  Jason replied 2 years ago.
Okay that's to low, you should be between 14.1 and 14.9, at 13 it's not really charging. Have you located the 50 amp fuse on the engine, an if so, is that fuse good?
Customer: replied 2 years ago.
It is charging, perhaps a bit low. I'm reading the current coming out of the battery (not going in), so I wouldn't expect it to be much higher than 12-13.
Yes, the 50 amp fuse is ok. I notice that if I pulled that fuse, the ground fault disappears. I assume that fuse is between the alternator and the battery.Do you understand what I mean when I say a "ground fault". It's not a "short circuit", but rather a "minor" leakage of current from a positive wire to another ground somewhere.
Expert:  Jason replied 2 years ago.
Do you understand what I mean when I say a "ground fault". It's not a "short circuit", but rather a "minor" leakage of current from a positive wire to another ground somewhere.
I don't think you understand what a ground fault is. This is all DC electricity you are working this, there is no such thing a ground fault in DC. In AC, where you have 3 wires, a Hot a neutral and a ground. A technical "short circuit" is when hot touches neutral. And a technical "ground fault" is when hot touches ground.
Since this is DC electricity lets try not to use the word ground fault. It is improper. With DC circuits there are only 3 possibilities. An open circuit, a short circuit, and a functioning circuit. And that's it.
The problem you are having is your charge voltage is to low. It needs to be 14 or better. Run the engine again, ground the meter negative lead to battery negative, and then check voltage at the 50 amp fuse. does voltage come up?
Customer: replied 2 years ago.
My chartplotter shows that it is only getting 10 volts from a fully charged battery. A short circuit would blow a fuse, an open circuit wouldn't allow it to turn on. Somewhere I'm loosing current (hence the term ground fault). I'm not making up the terminology. It's widely used in boating. It describes what I'm witnessing immediately (i.e., not after a period of time when a fully charged battery runs down). Thanks for the attempt to help, but I think its best to end this Q&A.
Expert:  Jason replied 2 years ago.
Your thinking of "Voltage Drop"....... Not ground fault. And really you are confusing yourself here because you don't understand what the words mean.
I will opt out.

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