Yanmar 2GM Ignition Source

[Peel]

I'm looking to add an engine hour gauge to my sailboat. It has a Yanmar 2GM20FC engine with SD20 Sail-Drive. It would be more convenient to pull the power from the engine area than trying to tap into the instrument cluster in the cockpit and run wiring from there. I've gone over the wiring schematics from the various PDF manuals I've found online, and it seems that the white wire coming off of the alternator (that isn't actually attached to anything) should be 12V ingition. But when I put a voltmeter between this and the ground bolt on the engine, I only see 0.3-0.5V when the ignition is turned on. The 55A alternator works fine for keeping the batteries charged. Am I missing something? Or is there a better place to pick up ignition power for the engine hour gauge?

[Wotname]

From memory, there isn't any 'ignition' wire in the engine harness, the only one is in the instrument panel harness.

I am not near my manual ATM to check but I will later.

[nuku34]

Not knowing the scheme for that particular engine, but having a bit of marine engine electrical experience, what you want for the hour meter is a source of +12vt power that only is active when the engine is running. The alternator is a good place to get that.
The main (big) alternator output wire is not the one you want as it will be generally connected the the start and/or house battery all the time that the main battery switches are “on” (assuming you are switching the + side of the batteries).
Often alternators will have a small wire going to the warning light on the control panel. I suggest you turn the engine on and check that white wire to see if its showing +12-14vts. If yes, then I think its ok to run the hour meter off that.
Other commentators may have different suggestions.

[Peel]

Originally Posted by Wotname

From memory, there isn't any 'ignition' wire in the engine harness, the only one is in the instrument panel harness.

I am not near my manual ATM to check but I will later.

By ignition, I mean a power source that’s only on when the engine ignition (key) is turned on. Most of the wires coming through the harness are for warning lights that have sensors between a hot wire and ground, so I can’t use them, or the fact that the hour meter will complete a circuit would also light the trouble light and alarm.

[Wotname]

Originally Posted by Peel

By ignition, I mean a power source that’s only on when the engine ignition (key) is turned on. Most of the wires coming through the harness are for warning lights that have sensors between a hot wire and ground, so I can’t use them, or the fact that the hour meter will complete a circuit would also light the trouble light and alarm.

Yes, I understand your description and question. I have attached a typical Yanmar GM series wiring diagram - yours might not be exactly the same but it should be very similar. If you have the stock Hitachi alternator (internally regulated) you could try connecting the hour meter in parallel with the R terminal on the alternator - usually a red/black wire going to the 'top' of a T shaped twin spade connector. The vertical aspect of the T shaped connector is the L terminal - usually a blue/black wire.

This should provide 12+ve anytime the key is on.

However a most esoteric method is to operate the hour meter via a Normally Closed (NC) contact on a relay that is wired in parallel with the low oil pressure (LOP) light. The relay is operated any time the LOP light is ON.

The hour meter circuit is +ve from an ignition wire and -ve via the NC relay contact. The hour meter runs anytime the ignition is ON and the engine has oil pressure.

[Peel]

Originally Posted by Wotname

However a most esoteric method is to operate the hour meter via a Normally Closed (NC) contact on a relay that is wired in parallel with the low oil pressure (LOP) light. The relay is operated any time the LOP light is ON.

The hour meter circuit is +ve from an ignition wire and -ve via the NC relay contact. The hour meter runs anytime the ignition is ON and the engine has oil pressure.

Interesting idea. So this would mean that simply having the key turned on wouldn't start the meter, only when the engine is actually running (producing oil pressure) would it actually be energized, correct?

[Wotname]

Originally Posted by Peel

Interesting idea. So this would mean that simply having the key turned on wouldn't start the meter, only when the engine is actually running (producing oil pressure) would it actually be energized, correct?

Yes, that is correct. It is a method routinely used in aviation (and elsewhere).

A little more effort initially to install of course but a more elegant arrangement IMO.

[Martkimwat]

I have a TinyTach digital tachometer/ hour meter which I fitted to my 2GM20 about five years back. it uses sensed pulses from one of the fuel supply pipes to sense RPM and when not running, displays engine hours. I will see if I can find the wiring diagram to see where it gets the engine hours information from. I seem to recall it is connected to one of the wires on the back of the engine start panel.

[GordMay]

Originally Posted by Martkimwat

I have a TinyTach digital tachometer/ hour meter which I fitted to my 2GM20 about five years back. it uses sensed pulses from one of the fuel supply pipes to sense RPM and when not running, displays engine hours. I will see if I can find the wiring diagram to see where it gets the engine hours information from. I seem to recall it is connected to one of the wires on the back of the engine start panel.

THE OP doesn't want to wire from the engine panel, as would be normal.

The Diesel Tiny-Tach Installation Instructions aren’t very useful, on this subject:
“External Power: External power is required to operate the unit. Vehicle power is most convenient, but any DC 12 VOLTS source may be used. From the black two wire power cable, connect the RED wire to the POSITIVE of the source and the BLACK wire to the NEGATIVE terminal of the source.”
➥ https://tinytach.com/installation-diesel

[BobHorn]

Not familiar with your engine, but on our Ford Lehman I added a NO oil pressure switch to power the hour meter. Our engine had a separate port on the block but you might be able to tee into the existing oil pressure switch or sender,

[Martkimwat]

Originally Posted by GordMay

THE OP doesn't want to wire from the engine panel, as would be normal.

The Diesel Tiny-Tach Installation Instructions aren’t very useful, on this subject:
“External Power: External power is required to operate the unit. Vehicle power is most convenient, but any DC 12 VOLTS source may be used. From the black two wire power cable, connect the RED wire to the POSITIVE of the source and the BLACK wire to the NEGATIVE terminal of the source.”
➥ https://tinytach.com/installation-diesel

I think you will find it's a lot easier to run a simple 12 volt supply from the battery (very small gauge wiring is fine) than trying to figure out which wire works on the alternator. In addition you get a digital tachometer as well which unless you have the 'B' type panel (horrendously expensive and not standard with a 2GM20), you do not have on a normal 'A' type Yanmar ignition/start panel, it is also very small and inexpensive. I have fitted mine in the recessed surround for my start panel. panel

[Peel]

My boat has the B panel, so already have the analog tach in the cockpit. But I like the digital one you mention if I needed to ever replace it.

Going to use Wotname's solution with the NC relay, assuming the white wire coming off of the alternator gives me the power that I hope it does.

[Wotname]

Originally Posted by Peel

My boat has the B panel, so already have the analog tach in the cockpit. But I like the digital one you mention if I needed to ever replace it.

Going to use Wotname's solution with the NC relay, assuming the white wire coming off of the alternator gives me the power that I hope it does.

If that white wire isn't already connected to anything and if it is just exiting the case of the alternator, then it may be the "W" wire and therefore unsuitable for your purpose. The "W" wire is used for tachometer sensing and will have about 5 to 7 V AC on it when the alternator is operating. The 2GM20 tachometer doesn't use this wire as it registers the RPM via a sensor near the flywheel.

Assuming the above is true in your instance, I would suggest referring back to post #5 and look for the red/black wire on the T shaped spade connector.

If your alternator doesn't have such a connector, try to post a picture of the alternator terminals (I know there isn't much space though).