Wiring a tach

[wiscoboater]

Hello,
I’m building a small mahogany runabout that will be powered by a 1959 Evinrude 18hp. I would like to mount a tach in the dash to monitor my motors RPM’s as I will be trying several different props to find my best speed within the motors RPM range. The tach i’m looking at is a standard Teleflex unit. I have never wired a tach to a small outboard like this one, and i’m not sure where to start with the wiring. Does anyone have a wiring diagram for this or know where I could look to find one?

Thank you

[fleetwin]

Boy, I just don’t think there is any good/easy/not messy way to wire up a tach for this engine, unless there is some new technology I’m not aware of.
Trying to run this single lead(s) back from the dash to the engine, then sneaking the lead(s) up into the mag plate, without wires getting pinched/broken/causing ignition problems, seems like a daunting task. Perhaps that tach lead(s) can be tied into one of the stop leads outside the mag plate though.
I surely understand wanting to use a tach to help pick the right prop, but I guess I would use a portable one for that, then forget about having a dash mounted tach. Later engines had leads built into the electric start wiring harness for tachs, making the wiring job much easier and more reliable. Not so for your engine.
Just my two cent opinion though.

[phil-b]

Most (all?) off the shelf dashboard tachs are made for either 4-stroke battery/coil based ignition (inboards or cars) or pickup from the alternator:

http://faria-instruments.com/site_manua … meters.pdf

And small old outboards are magneto based ignition, and lack alternators.

There’s a circuit out I’ve seen out on the web to adapt a 4-stroke battery ignition tach to use with magneto based outboards, but it required a 12V DC input.

In the 1960’s tachometers were made for magneto based outboards, but they’re hard to find (usually they had a meter and a "transmitter" or a special pickup which is often missing). Complete new old stock tachs are sometimes seen on ePay for $$$ (and you have to get the right one for your brand of outboard); Often what you see is just a meter (movement) from the dashboard, and the transmitter box has been lost.

I picked up an old airguide tachometer and transmitter on ePay, but it was flakey (loose connection), so I painfully extracted the circuitry (it was "potted" in epoxy and aquarium gravel to make the job hard), with the hope of reverse engineering it, and spent a month tinkering, but didn’t succeed. Then I started playing with making a transmitter for old tach panel meters using a tiny "AVR" microcontroller, but making something that people could easily adapt to their meter was daunting…..

[wedgie]

Have you considered a Tiny Tach ? I just ordered a knock off for under $15 Cdn. with free shipping. The real McCoy is around $45.00 USD. I’ll let you know how the knock off holds up.

http://www.amazon.ca/dp/B00CAKR18C/ref= … 00_TE_item

[frankr]

As already said, modern tachs won’t work on your motor. I suggest a Tiny Tach, which gets a signal from a wire wrapped around a spark plug wire. They look kind of funky in an old boat though. You might consider just mounting it in portable box.

[dave-bernard]

If you need on for testing I have a few merc-o-troni tach’s that work on any motor with plug wires.

[wiscoboater]

Thanks Dave, and everyone else. I did not know if it would work or not, question answered. I could see mounting that tiny tach below the gunnel by the motor control. That way it would be visible to me while running but not ruin the vintage look of the dash. I guess it will be just a big vintage looking speedo and a fuel gauge. I set the motor up with a single line fuel pump so I could use a permanent below deck gas tank.

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