Bought a boat a couple years ago. Motor only has 128 hours on it. Last 30 have been me in 2 years. Motor has run really good until yesterday, final run back to ramp and it went into limp/guardian mode. I put a vessel view on it and it threw a low voltage alarm. According to fish finders it only had 11.2v and from what I read about, the motor will go into limp mode if it runs WOT for an extended amount of time under 11.5V. Never got a low voltage alarm when starting the motor throughout the day. Even turned it off and turned it back on when it was in guardian mode and had 0 issues. Trim continued to work appropriately, even in guardian mode. Just once I got it on plane, it would shut down back to 3500 rpm and voltage never climbed when running down the lake. I knew something was wonky though because on that final run, I noticed the RPM gauge acting really funny and for split seconds needle would loose like 1000 rpm and then run for 3-4 min and then do it again. Finally, when it went into full guardian mode, nothing over 3500 RPM and it finally through that fault code on vessel view. In the past, when I would be running down the lake, I would notice that on the fish finders, the voltage would read between 13-14.3v. Yesterday, this didn't happen. Replaced the battery last summer, I ensured the battery I bought had the correct MCA for the motor. Never had any issues until yesterday. Anyone else run into this happening?

From what I find online, this is where I probably will start....
1) charge battery, ensure the battery has enough voltage for boat
2) put motor on muffs, turn it on, check power from red cable at the alternator and ground at battery to ensure 12v
3) Check that belt is not flapping and looks tight while motor is running
4) There is 100a fuse somewhere from the connection at the alternator to the battery, will ensure this is not blown.

Any other ideas before I dig into this lovely thing we call a boat?
Has anyone changed the alternator on one of these motors? If so, is it something I can do or best to take to a mechanic?

Since I have owned the motor, it has run like a champ for the 3 years. Only thing I had to do was replace spark plugs, replaced fuel filter, replaced water impeller, cleaned out strainer in lower cowling, installed vessel view and the motor has been flawless until now.

Also, I may mention, this might have been self induced. Went to the lake last weekend with a buddy and his dad. Got into a crappie bite that was unreal but unplanned as we didn't bring a cooler or anything to take fish home. His father and him caught their limits, we put them in the livewell but we didn't get home until midnight. So we plugged the boat into the onboard charger, left master power on, and let the recirculation pump run all night until the morning when they got up and cleaned the fish. It worked really well as all the crappie survived the night and they were fresh but this might of been a mistake on the electrical system. If so, I won't be doing that again, no matter how late it is when we get home. Just not sure how that could of caused issues with the alternator or charging system. Only thing I can think is maybe it caused some sort of reverse polarity and popped that 100a fuse? I don't know?

I would start by barrowing a starting battery from a fishing buddy that is known to work. If that does not resolve the issue, then you have at least eliminated the easiest part first. In addition, I don't care how new a battery is. I had a problem with depth finders turning off and acting like I had a loose ground, but the engine would start every time. Jacked with wiring and the problem would come and go for about a month. Checked the battery voltage, fine, took to an automotive shop, tests all passed. Finally bought a new starting battery. That solved the problem. Hopefully that's what it is.

Another thing to check is verify all ground wires are connected to the battery. I made that mistake one time and found one ground wire was hiding behind some other wires that I missed. Something to check and learn from my simple mistakes.

Ground ground ground... you were spot on my man. Except it was the ground battery from the alternator. The little flimsy wire terminal that is around the bolt snapped in half and my ground wire was just dangling right near the alternator. Replaced with a heavy duty gold plated one that won't flex and break and heat shrunk the connection. All is well, had the boat out twice and reading 14.3-14.6v when motor is on now. Super easy fix but I missed it twice when I took the cowling off. I was ready to get a new battery that morning and something came over me to just check all the wiring throughout the whole motor.

Thanks for the reply, it is greatly appreciated.