Tachometer wiring

[smithla]

About a year ago I purchased a ISSPRO tach from MMI. I finally got the boat back in the water, went to install it and discovered I had lost the paper work that came with it. Your wiring schematic shows one lead going to IGN and another going to the negative side of the coil.

Humm... the tach I have has four wires, red black,green and white. Could you please tell me which wires go to what points on the engine?

Thank you

Lance Smith

[Don Moyer]

Lance,

The red wire connects to switched DC power (like the ignition switch), the black wire to ground, the white wire to the negative of the coil, and green to the switched lead from the light switch.

Don

[ArtJ]

Moyer Tach not working

I have a black faced tach which I bought from MMI ten years ago.
IT has functioned perfectly till now. The wiring is, as mentioned earlier in
this post, red +12V, Black COM white to coil Negative.
This unit also has a pop out plastic plug in the rear.
I was replacing the steering cables on my quadrant this weekend and
the Tach wasn't functioning afterwards, possibly coincidental.
Also unfortunately, the radio shack vom i have quit ( this is the second one
to do so). Because of that and no wiring info, I couldn't troubleshoot other
than look at wire connections.

The needle just stays dead on zero. Is there a fuse inside the unit?

Any suggestions guys?

Thanks and Regards

Art

[ILikeRust]

The pop out plug is where an optional light goes, so you can have a lighted gauge for night time running.

I do not believe there is a fuse inside the unit, but of course I could be wrong. I just replaced several gauges today and none of them have a fuse inside (although I did not do a tach - I'm hoping my old one still works; if not, I'll be ordering a new one...).

Sounds to me like you might have knocked a wire loose somewhere, or possibly accidentally shorted between two terminals and blew a fuse somewhere. I would start looking at all the connections in the vicinity of where you were working and make sure they're all still good.

[ArtJ]

Thanks Bill
I will be checking it out today with a voltmeter and a scope if necessary.
I am assuming that I should see a square wave at the input from the
distributor. Early this season I installed Petronix ignition. I assume that
won't make any difference in what I see.

By the way, does anyone know which size a ten year old tach from Moyer
would be? I see 2 sizes in the catalog these days.

Thanks and Regards

Art

[roadnsky]

By the way, does anyone know which size a ten year old tach from Moyer
would be? I see 2 sizes in the catalog these days.

Art-
I'm pretty sure it's the 2" version.
A quick call to Ken would confirm that...

[ArtJ]

Thanks Jerry

I measured it and it is actually 3 1/4 inch diameter of cutout.

I checked this morning with a digital meter and found +12 volts between
Red and black at square connector pins. Also got a pulsating reading between
the white and black (gnd) pins. This lead me to believe that unless there
was a internal fuse, the instrument itself must be defective. I confirmed
my suspicion with Don Moyer. He also suggested that I disconnect the
plug in case the Tach might possibly short out the ignition. I did so.
He also offered to test the Tach on his boat. I need the tach for a trip
later this week, so I ordered a new one from Ken today. I will follow up
on the old instrument later .

Another strange occurance is that the original a/b both switch which has
been there forever, probably 40 years decided to fail and not shut off.
I can feel the unusual motion in the switch instead of a sold click.
I have ordered a new a/b switch to swap out. I don't consider this
related to the tach issue.
Regards

Art

[roadnsky]

I measured it and it is actually 3 1/4 inch diameter of cutout.

Ahhh, so this one...

PS - Isn't Don great?!

[ArtJ]

That's it Jerry.


Just some further possibly unrelated thoughts I thought I would throw
out anyways.
Do you think any extra protection diodes on the alternator or a xantrex
charging system could both back feed the Battery voltage when the
A/B switch is off? and possibly screw up the Tach.
Its just strange that the A/ B switch issue was noticed a week or so
before the tach died. Although, as I mentioned, the switch is 40 years
old and feels "bumpy" when turning off.

[roadnsky]

Do you think any extra protection diodes on the alternator or a xantrex
charging system could both back feed the Battery voltage when the
A/B switch is off? and possibly screw up the Tach.
Its just strange that the A/ B switch issue was noticed a week or so
before the tach died. Although, as I mentioned, the switch is 40 years
old and feels "bumpy" when turning off.

I'm gonna dodge that question and toss it over to our buddy Neil...

[ndutton]

I have no freaking idea!!

I kinda doubt it but I really dunno.

[roadnsky]

I have no freaking idea!!

See why I dodged it?!

[ArtJ]

When I get around to replacing the switch I will let you guys know.
Also, I will be replacing the tach later this week.

Sorry for the thoughts (just a frustrated EE).

[ndutton]

Please do report back, it's how we learn.

[ArtJ]

When I find out I will post and let you guys know.

Regards

Art

Most likely 10 year old bad tach and a worn out 40 yo a/b switch and unrelated.