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Discussion Starter #1 (Edited)
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.
 

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Forget Ohm for a bit. What do you have at the solenoid when the start button is pushed? If it is less than about 12.6 start cleaning contacts.
 

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Discussion Starter #3
Forget Ohm for a bit. What do you have at the solenoid when the start button is pushed? If it is less than about 12.6 start cleaning contacts.
Good point!

Unfortunately, it doesn't help any. I checked the voltage at the solenoid and I have 13.7v. All indicators are still pointing that the solenoid is the problem, except that when I powered it directly, it worked.

(Note: my original post said that I had 12.7 volts at the start button. Re-measuring this made me realize that was an error, it's actually 13.7. I'll update the original post, but no, you're not crazy, I originally said 12.7)
 

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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.
 
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Have you actually removed lugs from bolts, mechanically cleaned all surfaces, washers and lugs' ? (Unless the alt is energized ,,by the key,, start/stop the engine by independent curcuit should not cause a diode blowing surge. Having a button in the engine area can be handy for bleeding and other testing)
 

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Discussion Starter #6
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.
All that makes sense.

Unfortunately, it leaves me twisting in the wind on the topic of "what is the right way to fix this? I suppose I could start by cleaning all the connections and seeing if the start button will work again. If so, that would definitely answer the question.

I'm surprised that the solenoid would need to pull enough amps for this to be an issue. I thought that the entire point of a solenoid is to use a tiny amperage to control a much larger amperage. I would expect that even a small amperage through the button would be sufficient to close the solenoid. This is one of the things I HATE about the Internet: searching for this part returns a jillion vendors who want to sell it to me, but I can't find a single spec sheet that specifies the amperage required to close the solenoid.

The "pinhole" comment is interesting/unsettling to me. These old (original) wires are untinned copper, so any intrusion is going to corrode them pretty quickly. What you're suggesting is that a nearly invisible breach in the insulation could be sufficient to cause a lot of corrosion and render the wire too resistive to be useful. Of course, under those circumstances, I'd still see full voltage at the load end, as long as I don't try to pull any serious amperage. Frustrating.
 

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A few tests that I'd do, in addition to what you have done:

  • Does the solenoid circuit draw amps when the button is pushed?
  • Does the starter circuit draw amps when the button is pushed?
  • What happens if you manually jump the wires at the button ("hot wire" the thing)
 

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Seems you tested only one half the circuit, how are the returns i.e. the grounds are they clean and connected? Next what is the physical condition of all the wires in the circuit, not just the supply, corroded, clean then using the least abrasive method that gets the job done, frayed replace the wire, frayed wires cannot carry as much current. If all the wires are clean and not frayed and connected correctly, as stated above what is the the voltage at the solenoid when the button is pushed? If good it is the solenoid I don't know how many times in high school I ruined a screwdriver jumping a starter solenoid on a friends 69 Firebird, I know of two times we replaced the Craftsman screwdriver we used for it. Yeah I know tool abuse but when you get free unconditional replacements.....
 

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Discussion Starter #9
Have you actually removed lugs from bolts, mechanically cleaned all surfaces, washers and lugs' ? (Unless the alt is energized ,,by the key,, start/stop the engine by independent curcuit should not cause a diode blowing surge. Having a button in the engine area can be handy for bleeding and other testing)
I haven't done any cleaning so far, as (until this discussion) I didn't seriously consider corroded contacts to be a possible cause. Because (a) they don't _look_ that corroded and (b) I was assuming the amperage required to trigger the solenoid was low enough that a bit of corrosion wasn't going to make much difference.

If that's not the case, then cleaning the contacts is probably a good thing to try.

A little internet searching suggests using vinegar+salt to remove the corrosion, then neutralize the acid with baking soda. This sounds like a better idea than trying to sand everything. Thoughts?
 

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Discussion Starter #10
A few tests that I'd do, in addition to what you have done:

  • Does the solenoid circuit draw amps when the button is pushed?
  • Does the starter circuit draw amps when the button is pushed?
  • What happens if you manually jump the wires at the button ("hot wire" the thing)
Testing the amp draw on the solenoid and the starter is tough to do without help, so I haven't managed to do that yet.

When I manually jump the wire at the button, the result is the same as if I pushed the button (i.e. nothing happens)
 

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A solenoid allows a high amperage circuit to be energized by a low amperage circuit, nothing more. Take out the solenoid in an engine start circuit and you would need to run the battery cables to the starter button. Instead, you have a couple of #12 wires running from the switch to the solenoid, which has the battery cables attached for the starter. Push the start button and an electromagnet closes a circuit and the power can then flow through the battery cables.
 

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When I manually jump the wire at the button, the result is the same as if I pushed the button (i.e. nothing happens)
so I'd say you can eliminate the start button as the culprit.

and I'd say that your previous test seems to confirm that you can eliminate the starter/solenoid.

Testing the amp draw on the solenoid and the starter is tough to do without help, so I haven't managed to do that yet.
understand.

for the solenoid circuit you can measure the amp draw at the push button ... it would be fairly easy solo and the values would be the same as "at the solenoid".

Do I understand correctly that when you push start nothing at all happens? no click, no slow crank?
 

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Another thing in this line of discussion. Each of us should carry a remote start switch as pictured below to start the engine should the starting circuit fail. This can happen off the dock and if you have the remote start switch, it's less than a minute to hook it up and get the engine going!
 

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Forget ohms, if you hot wire the solenoid and it works then it is in the switch or switch wiring. Study up on using a voltage drop test. it allows you test every wire, connection or component with out removing any wires. it is simply reading the voltage drop at any point in the active circuit by placing the volt meter leads in parallel with the section that you want to test. tells you the voltage drop of the tested section.
https://www.freeasestudyguides.com/voltage-drop-test.html
 

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Discussion Starter #15
Do I understand correctly that when you push start nothing at all happens? no click, no slow crank?
To be very specific: nothing happens as far as I can tell ...

It's possible that the solenoid tries to close or something, but any noise that it makes is too quiet for me to hear from the cockpit.
 

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Discussion Starter #16
Forget ohms, if you hot wire the solenoid and it works then it is in the switch or switch wiring. Study up on using a voltage drop test. it allows you test every wire, connection or component with out removing any wires. it is simply reading the voltage drop at any point in the active circuit by placing the volt meter leads in parallel with the section that you want to test. tells you the voltage drop of the tested section.
https://www.freeasestudyguides.com/voltage-drop-test.html
I understand how to do that ... the problem is that it's really difficult to do single-handed.
 

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I understand how to do that ... the problem is that it's really difficult to do single-handed.
Very easy to do with long test leads and very hard to do the trouble shooting with out them. make a log test lead with a piece of wire
 

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Forget Ohm for a bit. What do you have at the solenoid when the start button is pushed? If it is less than about 12.6 start cleaning contacts.
Bingo!! I have seen many dirty contacts and bad switches that can pass a 0A voltage test easily but the minute they try to pass amperage, they fizzle out.

You can't test for this with the Ω setting of your DVM.... A volt-drop test on both the positive side and negative side of the circuit, under load, will give you the best information
 

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Relax ,trouble shooting this would be more difficult while dragging on a lee shore. If you don't have a fused button mounted in the engine area or the extendable wire unit Capta suggests . ???
 

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Another thing in this line of discussion. Each of us should carry a remote start switch as pictured below to start the engine should the starting circuit fail. This can happen off the dock and if you have the remote start switch, it's less than a minute to hook it up and get the engine going!
you are carrying a remote switch to be able to start the engine in a hurry why not just wire in the remote switch so you don't have to spend the time to connect it in a hurry. I was thinking of buying a second boat to tow behind so I would have a spare part for every thing on the boat with me.
 
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