Mysterious wire...

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RodS

RodS

Veteran Member
Joined
Apr 5, 2024
Messages
26
Location
Australia
Hi all, I have a mystery wire at my engine that I'm struggling to identify. It's a Lombardini 1503 and this red wire is hot when the key is on. It seems to want to lay along about to where the alternator is but as far as I can see the alternator has all the wires it needs. It sort of lines up with the starter as well. It has a broken off terminal on its end and I can't see any bolt or fitting that has a broken terminal on it. Engine runs fine, everything seems to work.
Cheers,
Rod
 

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Trace it back and see where it goes on the other end. If it's hot it must be connected to something. I'd suspect it's was for something that has since been removed, and it should have been removed too. Older boats often have a lot of "dead" wiring, but leaving one with an exposed energized end is just dumb.
 
jgwinks said:
Trace it back and see where it goes on the other end. If it's hot it must be connected to something. I'd suspect it's was for something that has since been removed, and it should have been removed too. Older boats often have a lot of "dead" wiring, but leaving one with an exposed energized end is just dumb.
Click to expand...
The wire is going back to his ignition switch. It’s hot when he turns on the ignition.

I can’t say what the wires purpose was. I would have guessed that it’s a field activation for the alternator.
 
I wish I had that wire recently. It is off the ignition run position and was for the original alternator exciter to get the ALT to charge. Your current ALT does not need it. Make note of this as you will find a need to activate something only when the engines are running. In my case it was DC2DC charger.
 
In our previous boat there was a #6 wire up under the flybridge that was hot, it was wired directly to the battery without any over current protection. You will find lots of wires going nowhere. I would tape it so it doesn’t short on anything and leave it for now. Maybe in the future you will find out what it was for l
 
I like the idea of tracing the wire back to the other end. Then, if reasonably convenient, disconnect it and lable both ends. As Steve said, you never know when a wire run may be useful.
 
If everything truly works then tape it off and leave it. Some how doubt “ everything “ works though.
 
tiltrider1 said:
The wire is going back to his ignition switch. It’s hot when he turns on the ignition.

I can’t say what the wires purpose was. I would have guessed that it’s a field activation for the alternator.
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This would be my guess but I was a bit thrown by the current alternator having all its wires intact. The wire runs back through the lume and ends up at the dash lights switch coming via the ignition. So it's key on power supply to the dash lights and whatever it was powering at the engine end. The only thing I can see that makes sense is alternator exciter wire but this alternator doesn't need it as you suggest, likely a replacement unit at some point. The alternator is putting out current.
Thanks for your input.
 
RodS said:
This would be my guess but I was a bit thrown by the current alternator having all its wires intact. The wire runs back through the lume and ends up at the dash lights switch coming via the ignition. So it's key on power supply to the dash lights and whatever it was powering at the engine end. The only thing I can see that makes sense is alternator exciter wire but this alternator doesn't need it as you suggest, likely a replacement unit at some point. The alternator is putting out current.
Thanks for your input.
Click to expand...
I’ll vote for this theory too.
 
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