I recently purchased a pontoon boat and on day #3 my motor died, I'm hoping to get some help from the community with correctly diagnosing and fixing the problem.
The motor - 1999 Yamaha 80hp four stroke (F80TLRX).
The problem - 30A fuse is blown, and when it's replaced the rectifier starts overheating (burning and smoking).
What happened - I was cruising along and started to increase throttle, but suddenly started losing power. With a minute or two the engine died, and I had no power to the tilt/trim motor (from either remote or engine side) or starter. One clue, or perhaps red herring, is that shortly before this occurred I tried turning on the fish finder. It didn't power up, which was odd, as it had worked previously before this cruise. Another clue/red herring, is that I found the electrical cable to the masthead light was under stress because of a broken seat cover.
Attempted solutions - My first step was checking the fuses, and the 30A fuse was blown. As mentioned the motor started smoking badly and emitting a burning smell when I replaced the fuse, which I confirmed was from the rectifier after removing some covers. I removed the in-line fuse connecting the fish finder, just in case that was causing a problem, and addressed the masthead light cable, but this didn't resolve anything. The battery is in good shape and the connections are clean and tight, and after inspection of the motor I can't find any loose/broken/chafed wires that might be the problem.
My first inclination is to just replace the rectifier, though if something is causing that to burn up I might just end up frying another one. Any suggestions for how to correctly identify and isolate the root cause would be greatly appreciated before I invest money in parts or a professional marine mechanic. (I may go with the latter in any case just to be on the safe side.)
Thanks in advance for any help offered.