2004 MerCruiser Black Scorpion 350 alternator and starter wiring

bschr287

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Mar 27, 2017
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We recently purchased a 2004 Centurion Enzo with the MerCruiser Black Scorpion 350 Motor. The previously owner had a new audio system installed and when looking at the wiring I have a concern. They added an isolator so that their starting battery was separate from the audio system but i'm not sure they hooked up the starting battery properly. I attached a drawing of the current wiring.

They have 6GA wire (white) running to the isolator, then 8GA wire running back toward the alternator that connects to the small orange 12GA wire with a butt connector. I lose the orange wire up in the motor harness but I noticed another 12GA orange wire comes out the other side and connects to the starter. I used a tester and the orange wires are connected (or the same wire) but i'm not sure if it's spliced to anything else.

My concerns come when I noticed the starting battery at the middle of the boat with 0GA wires running up to the starter/motor. This is the battery that clearly starts the boat but based on what I can see the orange 12GA wire is all that connects the starting battery to the alternator. The boat starts fine but can this small of a wire actually charge the battery back up?

Any input would be much appreciated.

On a side note - I am looking to improve the audio system so I plan to run 0GA wire from the alternator to the isolator, from there I will run 0GA wire to the two batteries/capacitors for the audio system. I had planned on leaving the second battery setup alone but not if it's going to cause problems going forward.
 

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alldodge

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Looks like the isolator is hooked up correctly

fetch


The ALT goes to the input side of the isolator. The sense lead of the ALT is connected to the Purple wire which connects back to the starter and back to the battery. A 10 gauge wire is normally used for charging circuit, and with added length going to a 6 is more then enough.

Going to 0 gauge is fine and a bit over kill, but won't be an issue
 

bschr287

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Mar 27, 2017
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Thanks for the reply ALLDODGE. My main concern was that the alternator was charging the battery through what appears to be a 12 gauge orange wire. This appears to be factory and must be normal. I will assume all is good.

Thank you!
 
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