Yanmar 4JH-DTE Electrical Reverse Engineering

[Microship]

HI folks...

Posting here after much Googlage to no avail. A few weeks ago, at about 5 AM, my outside helm engine panel (B-type) started shrieking. While I continued snoozing happily, dock neighbors came aboard and duct-taped over the Sonalert to shave a few annoying decibels... and once I flickered to life, we spent the day trying to find the problem. Despite turning up a few flaky connectors down in the engine compartment, we failed to figure out why the outside helm spontaneously had both 12V and a ground from one of the sensors.

Before digging further, I decided to move this to the top of the reverse-engineering priority list (I'm doing an 11x17 book of drawings for all boat systems, starting with existing stuff). I have the Yanmar service manual with the schematics for both types of panels (D-type in the pilot house and B-type at the helm, with a Y-cable laying under the engine that's probably the source of the problem), but am currently frustrated by a lack of information about the logic of the starter switch. This seems like a very silly question, but their schematic is rather inscrutable regarding what gets connected to what, and when. Some of the other devices, as well, are not shown functionally in their drawing... just wire colors boxes, some obvious, some not.

I'm doing a full schematic to current standards, which I'll be happy to share with y'all, but before I do, I want to be sure I'm not reinventing any wheels. Has anyone created a clear drawing of the Yanmar electrical system (or at least made a table that shows what interconnects correlate with the glow-off-on-start switch positions)? Debugging would be SO much easier...

Thanks much,
Steve

[svcambria]

I had this problem with a Yanmar C panel for a 4JH3; it wasn't a Yanmar problem at all, it was the Balmar voltage regulator for the engine alternator somehow passing current thru, so the panel thought I was enduring low oil pressure (even tho the engine was off, key was out, etc)...

Michael

[Microship]

Mmmm, interesting - thanks. I do have a Balmar... will peer at that side of things more closely!

Steve

[svcambria]

Quick check - pull the power plug on the face of the regulator. If the engine alarm stops, that's it...

Michael

[Blue Stocking]

Same alarm, different cause.
Ignition controlled, field current relay threw in the towel. Residual back feeding from 2nd alternator was enough to sound alarm.
When I turned ignition on, problem was nullified and alarm went silent.
Drove me bananas