Not too sure about the relay cuz I don't have one installed and never really looked at them, but it sounds like it takes less current to engage the starter and might be a touch more bulletproof. I don't believe the solenoids are very prone to failure tho either. I have certainly not had any issues since I re-wired mine last year.
To my eye, the most important thing you can do to avoid electrical issues with the Yanmar is pure and simple: get rid of all the original Yanmarwiring wherever possible!
I rewired my entire engine last year along with the solenoid wire. I ripped out the untinned Yanmar wiring harness and ran my own system using bus bars. Hard to believe the wire Yanmar used, at least on my 2004 3gm, was so poor. After less than 10 years in a clean engineenvironment with dry bilges, the wiring harness just crumbled in my hands.
I also found there to be a lot of harness wires that were just floating around, not being used.
yeah I was hopeful that I could re-use the wiring, but the more I looked at it the more I realized how badly it needed an upgrading. Mine is about 20 years old and should have been replaced many moons ago
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