Thread: 25 HP Tohatsu Magneto/ Gen Problem

ok.... let me explain the system somewhat. The yellow and white wires are the same. Think of it as one single strand of wire wrapped around a nail under the flywheel. The fact that you have low resistance between the two ends is good. The fact that you aren't getting a measurable ohm reading to ground is good. The reason the voltage is about half value when checked to ground is due to the diodes working in the rectifier/regulator. The reason you are getting low A/C voltage readings is due to the type of meter you are using. A DVA meter would show much higher readings. It's basically a peak meter. I can only assume at this point but from what you have described so far, the charging system is operating as it should. It is not a high amp charging system. I forget the specs but as I recall, it's like a 5 amp alternator at 6000rpm. Output tests at idle or slightly above will yield low values as expected. Don't expect it to charge a deeply discharged battery in a few short runs across the lake.
If I apply what I know and the most common complaints I get specific to this topic, I would "guestimate" that you are either running several power draining devices off of a small battery and not charging between trips or your battery has a weak cell or possibly a combination of the two.
In any event, please don't take offense to anyone questioning your ability to diagnose this issue. If you were fully aware of how the system works and how to diagnose it, you wouldn't be here. And I think most folks understand that.

Now, I will throw caution to the wind here based upon an earlier statement. You mentioned earlier about pulling the flywheel. I am strongly recommending that you not do that. There's nothing you can test under the flywheel that you can't test otherwise. And here's the reason. The later model 25s like yours came with magnets that were glued in with a different type of epoxy than earlier models. That epoxy has a bad track record of letting go and allowing the magnet to wreck havoc on the stator assembly. Even if you have the proper puller, you run the risk of compromising the already fragile magnet/epoxy union. If you use a makeshift puller and a hammer, your chances of creating a costly repair increase greatly.

As always, Good luck
Sliderman aka The BOAT DOCk

Be open minded to looking for parasitic drain in the system. Lights, radio's, etc. Undo the positive cable and set up the meter to read dc amps. See if you have a power drain. Something is amiss.