Well I finally got around to building this circuit. It did not work. I have some more info though that could shed some light. I'm close to giving up on this, but dangit there has to be a way!

The circuit I built above does provide power to the hourmeter and the meter works....however, it works with just the ignition key ON and the engine still off....which is what I was trying to avoid. So, i've learned that the 5.4-5.6V tach signal is only when the engine is running. When the engine is off, the lead from the tach is reading 11.25V while the lead from the ignition key is reading 12.10V. So I guess because of this, since the tach lead has almost 12V with the key ON/engine off, thus not switching the transistor?

I feel we are close!

 

What circuit did you try?

So the tach signal goes low when running? High when motor off?

Then this is close.

 

What circuit did you try?

So the tach signal goes low when running? High when motor off?

Then this is close.

I built the circuit in your last post. With a 2N3904. And yes....it seems the tach signal is low when running and high when motor is off.

 

I built the circuit in your last post. With a 2N3904. And yes....it seems the tach signal is low when running and high when motor is off.

I didn't know that at the time. Only that there was a voltage when running.

Sorry!

 

I didn't know that at the time. Only that there was a voltage when running.

Sorry!

no problem at all! I actually didnt figure out that part of the puzzle until I just went out and fiddled some more. I'll give your schematic a go and see what happens this time around. thanks again for all your help.....when this finally works it will be glorious!!!!!

 

What circuit did you try?

So the tach signal goes low when running? High when motor off?

Then this is close.

another thing, is the transistor in the new schematic a NPN or a PNP?

 

PNP

Maybe someone else can simulate it for you.
Hope I haven't scared them off!

I'm more of a try and see type, and have not built this.

There is so much that I still don't know about your circuit. Like the pulse width of the tach signal.

 

For the few bucks it costs to make, I don't mind experimenting at all. as far as the tach signal....ummmm, yeah.....way above my head

 

Hmm...that could work. The motor is an EFI, so fuel pump runs in ON position, so that's out. Thanks!

If it does then it is incorrect, fuel pump should run on EFI systems for max 3 seconds when igniion switched on to prime the system. After that the pump relay should only operate when an engine ECU receives a pulse indicating that the engine is turning. This is mandatory on all automotive EFI systems and I suspect marine systems too. The reason for it is that the fuel pump stops pumping in the event of a burst fuel line or serious leak , resulting in engine stall.
PS Connection to fuel pump supply circuit is ideal for your engine hour meter.