Mercury outboard

We have a 25hp Mercury outboard that is not charging the battery.
Can anyone supply a diagnostic for this application? We do not have
any manual.
Reply to
bobelon
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I assume you don't see a rise in voltage across ther battery with the engine running. You have a very primative chatrging system. There is a coil under the flywheel and a bridge rectifier mounted in a potted block somewhere on the motor (location varies by model) trace the red wire back from the starter to a block with 2 yellow wires that dissapear under the flywheel. That is the rectifier. There are only 2 parts. If you have 16-20 VAC on the yellow wires you are lucky and you just need a recrtifier. No volts on the yellows and you probably need a stator. I can probably come up with the correct ohm readings across the stator but my guess is a bad one will read open or shorted to ground. I think it should be 400 ohms or so but that is a rusty memory. I do have a book at home.
BTW I have just used a big block bridge rectifier for the $40 mercury part but that is not the recomended fix On these little 9a charging systems they do not have a regulator. That kicks in with the 16a system.
Reply to
gfretwell
Thanks, Just what I was looking for, some color codes.
Reply to
bobelon
I seem to remember now that an ohm reading on the charging coil is low, an ohm or so, the "couple hundred" is the ignition side.
Reply to
gfretwell

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