Yanmar 4JH57 will not power down

[Randy Nevada]

We are currently spending the summer cruising season in Grenada. Been here a week and so far so good. After flawless engine performance on the trip down here we were surprised to find the starboard engine powered up when we got back to the boat after supper. I tried to power it down with a long press of the power button but no joy. The engine was still powered up. A quick press of the start button and I was relived to hear the engine start and run normally. The stop switch also worked. I finally had to power down the engine with the main power switch, hoping that once I turned it back on all would be normal. Well turning the main big red engine power switch back on powered up the engine with out any input from the power button.

This morning thinking that the issue might be the Yanmar instrument panel I switched the starboard and port panels. This did not affect the problem. The starboard engine is still stuck in a power on state but it runs and stops normally.

There isn't much circuitry between the instrument panel and the ECU. Its hard to tell from the system diagrams but it looks like the accessory relay may play a role here. It seem odd that it would fail closed.

I would love any advice before I throw myself on the mercy of the local Yanmar dealer here in Grenada.

Cheers
Randy
High Sierra (Leopard L47)