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post #4 of Old 08-15-2019
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Re: Starting Circuit Mystery (why won't my engine crank?)

Just like a car, you can turn on the headlights and they are nice and strong, but you can't start the car.
A bad connection may pass a low amperage draw, the headlights, but not a high one like a starter. Somewhere in your system, you have a bad connection. When it happened to me I just ran new wires directly from the switch to the starter and cut out the run through the key and harness. Sure I can now start the engine without the key, but I don't because I know that if I do, I might burn out a diode in the alternator.
Most often though, it is the engine ground which is at fault. A bad connection, a bad crimp on a lug, or too many wires on the same bolt. Especially on a boat in saltwater, a pinhole or cut in an out of sight place in a wire can corrode a wire enough to break the connection over time. These are particularly hard to find as they can be behind paneling or in a harness.

"Any idiot can make a boat go; it takes a sailor to stop one." Spike Africa aboard the schooner Wanderer in Sausalito, Ca. 1964.
“Believe me, my young friend, there is nothing - absolutely nothing - half so much worth doing as simply messing about in boats.” ― Kenneth Grahame, The Wind in the Willows

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