Can my tach be hooked back up?

[Airxsteel]

I had a mechanic tell me that my tach could not be hooked up. I kinda looked at him like he was crazy. I don't understand how the tach can not be hooked up.

I bought an old boat and the previous owner cut the tach. 1979 140 HP Johnson V4. I don't see any wires coming from the motor however. My thinking is that he didn't want to worry with it, and easiest thing to do to get me out of the shop was to say it wasn't fixable.

Now I am no gear head by any means, but seems to me , EVERYTHING is fixable.

I don't know if the tach even works, but that isn't an issue, I can get a simple tach and put on there. I guess the real issue is the wiring from the motor to the guage.
Is this something that can be done easily for a boat mechanic?

Thanks,
Eric

[luvdmymerc]

If your charging system is working properly, and the gage is working properly, you
should be good to go. Just need to run the proper wires.

[Airxsteel]

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by luvmymerc &raquo;</TD></TR><TR><TD CLASS="quote">If your charging system is working properly, .</TD></TR></TABLE>

What would this be , the rectifier?

[jimh]

Your motor likely has a permanent magnet alternator to provide electrical current for charging. A permanent magnet alternator has rotating magnets and a stationary coil, often called a stator. The output from the stator is an alternating current. This is connected to a rectifier in order to convert it to a direct current.

The tachometer signal is derived from the charging system. The tachometer signal is usually obtained from a half-wave rectifier tap. The tachometer signal thus is a string of pulses whose frequency is proportional to the engine speed, and whose voltage is clamped between about 1-volt and the battery terminal voltage, typically around 14-volts.

The tachometer integrates this pulse train and develops a meter reading proportional to its frequency. In order that the tachometer be accurate, there is often an adjustment to allow for differences in the number of magnets in the permanent magnet alternator and the number of poles in the stator coil winding.

So long as your motor has a functioning charging system, it should be possible to derive a tachometer signal from it. It should be possible to obtain a tachometer which can be adjusted to match the frequency of your tachometer signal, thus giving accurate engine speed readings.

[Airxsteel]

Clear as mud!



No , I follow you. So as long as those components work, then we are good to go.

Like on that show "Dumb and Dumber" when Lloyd was asking Mrs. Swanson what the odds were of them getting together and she said "Million to 1" , Lloyds response was..............

"So your saying theres a chance.........YES"

[JAXFLRANGER481VS]

Dang bro, you got a brain on ya. That was cool.

All the best,

Tom

[JoshKeller]

On your wiring harness, look for the grey wire. thats the one that feeds the tach the signal. I jumped mine fromt he key and run a wire to the tach. There should also be a ground, and a positive for the back light. I'll look at my '78 tomorrow and get the wire colors for you.

[Airxsteel]

I have no grey wire coming off the motor, or if there is one, I can't find it.

[Airxsteel]

Here is the wire coming off the tach:


Here is the wire coming out of the bottom of the control box:


And here is my motor wiring, I don't have a clue: