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

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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?

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.

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.

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.

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 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!!!!!!!!!
  3. Loren Beach's Avatar
    Takes me a while to figure out what I do and do not know.
    Did you still run a ground cable to the original bolt on the bell housing?

    Also, it looks like you kept the original harness wiring, but just eliminated the trouble-prone connectors. Is that correct?

    If replacing the harness I note that the original wired were coded by function. Last week I asked my local electronics repair shop if they carried wire in some/all of the odd colors and stripes used by Universal for the original harness.
    They do not, and advocate labeling both ends if I decide to run new wires. Sounds reasonable, absent any ready source of all those odd colors.
  4. Christian Williams's Avatar
    Hi Loren,

    I just took all the random grounds off the engine block and moved them to a new bus bar on the engine stringer (TAFG molding). That bus bar is wired to an ear of the starter motor.

    On the harness, I replaced only the terminals in most cases. Far as I could see the wires were fine. The color coding all over the boat is really useful, and still corresponds to the factory schematic in most cases.

    Any new wires or wire extensions I add are yellow, which at least reminds me I was the one who did it. It seems to me that it's the old (beat up, cheap, jury-rigged, inexpertly done, rusted, broken) ring and spade connectors that cause trouble, get loose, wear out.

    I did use some new wire between instruments on the back of the cockpit panel, because they're short wires and it was easy. Color coding doesn't seem so necessary there.

    As you know, I'm entirely self-taught when it comes to DC systems. I make sure to eventually get an electrician to look at the work. He always says "I use new wire througout." I can see why a professional does--and why I don't.
  5. Geoff W.'s Avatar
    Christian, did you use the 150A Bus Bar from Blue Seas? I see there is that one, and one that goes up to 600A... I bought the 150A one and if there aren't issues on your boat with it, that's good for me.