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post #1 of Old 08-15-2019 Thread Starter
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Starting Circuit Mystery (why won't my engine crank?)

This is the 1979 Westerbeke 40 diesel on my Tartan 37.

Short version of the question. Pushing the start button does nothing, but I've tested each part of the circuit individually and can't find the failed component.

Long version:
See attached simplified diagram:
Pushing the start button does not crank the starter. I've methodically tested everything:
1) If I supply power directly to terminal B on the solenoid, the engine starts ... to me, this demonstrates that both the solenoid AND the starter are working.
2) Putting a meter at either end of the wire between the solenoid and the button, I get near 0 ohms resistance
3) Putting a meter on the pushbutton, it shows infinite ohms when unpushed, and near 0 ohms when pushed
4) Putting a meter on the 12v supply to the pushbutton, I have about 13.6v, which is what I would expect.

So, it _appears_ as if all the parts of the system are working, but for some reason they aren't working together.

My best guess is that the solenoid is old enough that it's not quite working corectly. Such that the amperage that comes through the pushbutton is insufficient to close it, but when I jump to it directly there are enough amps to make it work. Is that something that happens with older solenoids or am I full of it?

I'd like a way to verify that this is the problem before I dump $40 on a replacement solenoid.

Thanks in advance for any advice.
Attached Images
File Type: png StartCircuit.png (21.1 KB, 19 views)

Last edited by BillMoran; 08-15-2019 at 10:32 AM.
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