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Discussion Starter #1
My 460 is in a 1995 jet boat. I've been struggling to get the batteries charging. I initially replaced the alternator but no change. When not running, the meter shows battery voltage at the back of alternator indicating a good connection. When running, the meter shows .4 -.6 volts at the back of the alternator. When I bypass the connections and run the negative post on alternator to ground, it shuts down the engine. I took the alternator back and it tested good. Any help would be greatly appreciated.
 

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It sounds like you have a harness issue.
What brand alternator and model number.
Try running new wires temporarily to battery and ground.
Boats notorious for corrosion in harnesses and switches.
 

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Don't think that a new alternator can't be bad out of the box. I had to go through 5 one time from a reliable parts house, They said that sometimes they get them like that.
 

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1 wire Alternator? My thought is corrosion in circuit. Measure voltage while working. No load testing will show full voltage if there is any continuityget it running keasire from post of alt to case. Then post of alt to battery. The voltage wire (if not 1 wire) to ign source/controller
 

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I would not run one wire in a boat, I'd use a 3 wire setup so the alternator can sense load from where ever the main power connection would be. Also, "batteries" - should have a battery manager is running more than one, just tieing them together can results in one hot and one dead, or much of nothing. Been there, been adrift with that.
 

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Discussion Starter #7
Thanks for the help everybody. It's a Wilson two post marine alternator. The two posts are labeled positive and negative. I am more confused than ever after tracing the wires and looking at the diagram that came with the boat in the 460 manual. The harness connection has a fat red wire which is clearly the output, then a thin purple wire (followed it and goes out to the electric choke then on to ignition switch and instruments) and a blue wire (constant voltage) that someone cut off at some point. The old owner had the fat red on the positive terminal and the thin purple choke / ignition on the negative. Clearly, the wire that goes to the electric choke doesn't belong on the negative terminal, right? The weird thing is that testing that wire shows continuity with ground but I don't see anywhere where it is grounded along its length. I'm afraid I'll short everything out if I hook up current to it. Is seems like this might explain why the engine dies when I ground the negative terminal on the alternator if it's grounding the ignition wire, but then why is it not doing it from the start if I have continuity with ground on that wire. The Ford diagram seems to indicate that the purple electric choke / ignition wire should be hooked up to stator output on the alternator. Is that correct? Since mine only has the positive and negative posts do I need a different alternator or is there a way to make this work? By the way, the harness did not have any ground wire for the alternator so I'm totally confused. Any insight is greatly appreciated. Thanks!
 

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Choke wire goes with the red wire. (Ground / continuity is through the choke heating element.) Need to add a ground strap from alternator negative to engine block and battery negative.
 

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Just a thought? Maybe your car/truck wasn't asking for any energy battery fully charged?
Just a thought
tim
 
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