3YM30 starter doesn't engage

[Boater Sam]

it seems that part number 128990-77550 is the more recent one. Hopefully they've fixed whatever issue it had. Plus, I'm still puzzled why the
panel would have gone black. Unless activating the relay cause a short somehow.

That is still puzzling me too.
If it was a short something would have got distressed and hot.
I still think that it is a poor connection somewhere that will not pass the current needed for the solenoid to pull in, it is quite high.
I would carefully check all the connections and cable crimps that are on the back of the starter motor, that is all the positive feeds and similarly all the negative connections, a bad contact or termination on either will cause the voltage to disappear at the panel.
Engine vibration can do odd things to electrical wiring causing intermittent connections .
An interesting fault, but not for you !

 

[VicS]

It seems the problem is an intermittent fault in the starter relay (24 in diagram, pictured in post #36).

Following up on post #55, that test was flawed because the manual starter switch was installed by removing the small white wire attached to the solenoid on top of the starter. Thus when the relay was jumped, nothing happened. Removing the remote starter switch and re-attaching the small white wire resulted in the engine starting as normal from the panel.

So as Koeketiene pointed out, these Yanmar relays are said to have problems. I'm going to buy, but of the two numbers

it seems that part number 128990-77550 is the more recent one. Hopefully they've fixed whatever issue it had. Plus, I'm still puzzled why the
panel would have gone black. Unless activating the relay cause a short somehow.

I have had a look back at all your earlier posts in the thread

I think Id missed the implication of what you said in #31 about the white wire "just inches away" and taking that in conjunction with what you said in # 59 yesterday evening I think there is a good chance there is a bad connection to the relay or even that the rely is defective after all

However neither of these would explain the behavior of the panel warning lights which you first reported ........ there may be another defect or bad connection. temporarily corrected but waiting to cause further trouble.

I think I would now check all connections on and around the relay and possible and check the operation, or otherwise, of the relay carefully

 

[farmer.leo]

However neither of these would explain the behavior of the panel warning lights which you first reported ........ there may be another defect or bad connection. temporarily corrected but waiting to cause further trouble.

Right, one intermittent problem lurking behind another. Because there was nothing consciously done to correct the initial problem.

It's nice to now understand more about how the starting system is supposed to work, and how I could jump start with a screw driver if needed sometime.
But it would be nicer still to know what caused it and that it was really fixed.

Thanks to everyone for your generous help and knowledge! If I learn more I'll report back.

 

[KAM]

Just got the same problem. Measuring resistance across the starter relay over many applications it's varying from open circuit to random ohms to zero. As was said earlier must be a common fault. Have to say this is the first fault I have had on the engine over 1500 hours and 13 years. Can't see why an automotive equivalent won't be satisfactory. The relay is nicely marinised and mounted on av mounts but cant see the point of having it attached to the engine and subject to extreme vibration when it could easily be mounted elsewhere. Should probably be a lifed item and replaced at ??? hours before it fails.