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M25 Engine Wiring Upgrade Part 2--Alternator Jump and Bus Bar

Rating: 2 votes, 5.00 average.
One way for a boat owner to look at his yacht engine, when neither a diesel mechanic or master electrician, is as something to look at. We know at a glance if a boat is fast or seaworthy without being naval architects. We can conclude in a moment, even from a distance, if a suit of sails is trimmed properly, and altogether that's the aesthetic of sailing--if it looks good, it probably is good. True, It takes experience to judge a yacht. It takes much less to judge the outside of a diesel engine.

What's wrong with this picture of my M25?
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Well, for starters, I'd say the wires are kind of messy. And I don't really know what they all do. The engine was formerly rustier and dirtier, but the current owner ( me) got in there with rags and brush and solvent and cleaned it up some. All those grounds on the engine block look pretty random. Are the ring connectors the right size? The trailer connector, which joins the engine harness to the cockpit instruments, seems OK--but trailer connectors have a bad reputation. Is that plastic in-line fuse holder original, and therefore 28 years old? That 25A fuse is about the biggest on the boat. Many of the wires have engine paint overspray on them, which looks lazy. At least the alternator bracket is of the newer type, so that upgrade has been done. The coolant tank cap is new. There's no black dust from a deteriorating or misaligned alternator belt. The engine works fine at the moment, but even a casual look suggests the wiring will never get out of the chorus line. Runs 10, Looks 3.

Three good engine tutorials are Metzger, Maine Sail, and Stu Jackson's Critical Upgrades. There are many other threads on forums and Google that make understanding and sprucing up the little iron horse no harder than tuning your rig or varnishing a board. Twenty years ago all this was a secret. Today anyone can apprentice to the masters.
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In doing my upgrades, many ring terminals revealed themselves in bad shape.The terminal for the heavy ground in the right photo above came off in my hand. You can't see this at a glance, it only becomes apparent when your hands are dirty. I removed the trailer connector and replaced it with butt connectors. Maybe necessary, maybe not, but in any case easy to do. The recurring tasks of stripping wire and shrinking terminals make good tools essential.

I did the alternator jump recommended in the tutorials above, which requires a hefty wire. So I bought an 18-inch battery cable from West Marinewhich turned out to be too long. My electrical kit can only handle up to #10 gauge stuff. I didn't feel like buying the gear to make battery connectors, so I begged a friendly rigger to cut it down and put on the right connectors. This took three phone calls and two trips to his shop. The alternator jump sends the charging current to the house bank without having to travel first to an ammeter in the cockpit, a round trip which adds unwanted resistance. Because my wire is black but positive, I wrapped it with red tape.

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Now the trailer connector is gone, old in-line fuse and wire clips are upgraded and extraneous wires deleted. The most important change was in me--I now know what each wire does, where it goes, and why it's there. If things go wrong, I'll at least know what it's not, if not what it is.

A negative bus bar is now mounted on the engine stringer.
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It's just a way to get the grounds off the engine, and theoretically may make for happier electrons. It connects to the mounting ear of the starter motor, and that called for a hefty cable similar to the alternator jumper. But this time I wised up. There are several on-line companies that sell stock cable lengths with terminals of various sizes, and this #1 gauge cable cost $9 instead of $24 and a favor. They'll also make a custom length for less than it would cause to equip yourself to install batteries in a cruise ship.

Ever try to touch up rust spots on an engine using Universal bronze spray paint? Either you spend a good deal of time masking, or everything else gets painted too. A simple solution is to spray some paint into a clean tin can, then use a foam brush to dab it on the engine. I put a rag over the can when spraying into it, because otherwise your eyebrows turn Universal bronze too. And you have to dab fast, because drying is rapid.

Sure, it's still just a three-cylinder 21-horsepower tractor engine sentenced forever to plow an ocean that won't furrow. But it's been running for 1,663 hours so far, and with luck and a wink and occasional zinc, might just make it longer than we do.

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  1. Rick R.'s Avatar
    Ok, now that you've made it look so easy, I have no choice but to just DO IT! Thanks for the great how-to...
  2. hdlEric's Avatar
    THANKS SO MUCH for this info!!!! When I recently encountered a problem with my starter switch, I was panicked, and didn't know where to start!! This information has saved me lots of time researching details about electricity that I just cannot seem to grasp. It just tells me how to do it, with some relevant info.
    thanks again!!!!!!!!!