Yanmar 3jh4e alternator overcharging

[Wotname]

Originally Posted by Henry Walker

Have found a 4.3 ohm resistance on neg wire to panel. Tracked it to this thing at the the back of the engine. 4.3 resistance between the two terminals marked red. Is this significant? What does this thing do?. Starter relay??

Alternators both internally regulated. Both work fine. Pretty sure they are not the problem. No access to external regulator here.

It is unlikely to be your problem as it has been connected all the time before the current fault developed.

I am also assuming it isn't connected in series with the neg wire to the panel as that would make no sense at all. The neg wire is probably simply providing the neg return for the relay you found. To confirm what it is, follow the other small wire on the item. This will lead to whatever activates this relay. Or follow the two large wires as they will take you the item which is activated by the relay.

[Scubaseas]

"What does this thing do?. Starter relay??"
Sorry didn't see the picture. It does look like a solenoid.

Connect yellow and brown stripe wire to yellow and brown striped wire.

Red is probably B+ or hot all the time. Back is likely a ground. Yellow/brown wire is the one that goes from starter button or ignition switch to starter solenoid.