Tach and 3 wire

sgtjd

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I needed to replace/rebuild my Tach on a 1973 Mach I with 351C. When I did some research I found that tach man can do it and he has a three wire tach. Mine has two wires. What is the reason and purpose of the 3 Wire tach. Is it good for me? I do have a pertronix coil II and electronic points.

 

MechEng

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Here is a good article that explains the three wire set-up:

http://www.classic-cougar.com/images/storepics/8000rpmtach/3wiretachinstructions.pdf

The stock Tach is basically a current measuring device that uses the voltage flowing through it to the coil to raise the needle the correct amount. It's not super accurate, but it does work. The three wire is powered directly from the battery and senses the trigger pulses going to the ignition coil. This is helpful to people who want to upgrade their ignition because it allows for a full 12v ignition to be used instead of the 6V style our Mustangs come with from the factory.

 

TheRktmn

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That article is a copy my original conversion tach wiring instructions from 2005! I'm surprised that a copy is still around.

As MechEng stated, the OEM tach is wired as an integral part of the ignition system. If the electrical part of it dies your car will not run. My three wire tachs are not a part of the ignition circuit and work with points, Pertronix, MSD, Duraspark, Mallory and many other ignition systems.

Here is a basic drawing of how the factory tachs are wired and why they can cause issues: http://www.classiccougargarage.net/showthread.php?tid=86

I have been converting tachs and making OEM style tachs for cars that did not have a tach since 2005. My tach conversions come with a lifetime warranty and are so good that another shop asked me to do conversions for him, then disassembled them and tried to buy my custom parts from the vendor using my part numbers!

I stand behind all of my products and if you are considering a three wire conversion I hope you will look at my offerings before choosing a vendor.

My website: http://www.rccinnovations.com

 
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turtle5353

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Bob (rocketman) did my tach about a year ago, and it is flawless and works great and looks great. Couldn't ask for more! Price is good also and he answered any and all questions I had. You wont go wrong with one of his conversions. And you don't have to worry about your car just shutting down with the old tach in place.

 

rvrtrash

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I highly recommend him as well. He did a 71-73 Tach and '68 ammeter for me, and am happy with both.

Steve

 

sgtjd

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That article is a copy my original conversion tach wiring instructions from 2005! I'm surprised that a copy is still around.

As MechEng stated, the OEM tach is wired as an integral part of the ignition system. If the electrical part of it dies your car will not run. My three wire tachs are not a part of the ignition circuit and work with points, Pertronix, MSD, Duraspark, Mallory and many other ignition systems.

Here is a basic drawing of how the factory tachs are wired and why they can cause issues: http://www.classiccougargarage.net/showthread.php?tid=86

I have been converting tachs and making OEM style tachs for cars that did not have a tach since 2005. My tach conversions come with a lifetime warranty and are so good that another shop asked me to do conversions for him, then disassembled them and tried to buy my custom parts from the vendor using my part numbers!

I stand behind all of my products and if you are considering a three wire conversion I hope you will look at my offerings before choosing a vendor.

My website: http://www.rccinnovations.com
thanks for the Info and now I have some great resources. I do have it ready to go. I'll check your site and let you know. thanks everyone.

 

Andreas1973MustangMach1

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Hi

I bought the 3 wire gauge too. What will happen with the stock coil sensor wire? Or is it for an other gauge?

 

TheRktmn

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The stock wire is the power lead to the coil. You need to put a jumper across the connector to complete the circuit without the tachometer.

 

will e

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I just installed my Rocketman's converted tach a week or so ago. It works great. Wiring was a breeze. As he indicated above, I just spliced the original tach wires together. This would be a great place to insert a 'kill switch'.

Rocketman was great to work with. Turn around was fast and his packaging was awesome.

 
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Manu Mach1

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73 Ford Mustang Sprint from Mexico.
My next purchase will be this tachometer from Rocketman, to replace the idiot light :)

 
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Mesozoic

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That article is a copy my original conversion tach wiring instructions from 2005! I'm surprised that a copy is still around.

As MechEng stated, the OEM tach is wired as an integral part of the ignition system. If the electrical part of it dies your car will not run. My three wire tachs are not a part of the ignition circuit and work with points, Pertronix, MSD, Duraspark, Mallory and many other ignition systems.

Here is a basic drawing of how the factory tachs are wired and why they can cause issues: http://www.classiccougargarage.net/showthread.php?tid=86

I have been converting tachs and making OEM style tachs for cars that did not have a tach since 2005. My tach conversions come with a lifetime warranty and are so good that another shop asked me to do conversions for him, then disassembled them and tried to buy my custom parts from the vendor using my part numbers!

I stand behind all of my products and if you are considering a three wire conversion I hope you will look at my offerings before choosing a vendor.

My website: http://www.rccinnovations.com
That's awful that someone tried to reverse engineer your work - it really just shows how pervasive greed is in the world.

I've also got the RCCI (Rocketman's Classic Cougar Innovations) modified tach in my '71. I ran without a tach for many years (almost 10 years, actually) until I realized that I could simply have my stock tach upgraded with modern electronics. Works great and it is also DEAD ACCURATE, I've verified this using the 36-1 trigger wheel and the crank position sensor. Love the fact that the appearance is stock as I was seriously considering doing a wholesale replacement of the gauges with aftermarket units. I also have had my fuel gauge recalibrated and it reads accurately once again. ::beer::

 

TommyK

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That article is a copy my original conversion tach wiring instructions from 2005! I'm surprised that a copy is still around.

As MechEng stated, the OEM tach is wired as an integral part of the ignition system. If the electrical part of it dies your car will not run. My three wire tachs are not a part of the ignition circuit and work with points, Pertronix, MSD, Duraspark, Mallory and many other ignition systems.

Here is a basic drawing of how the factory tachs are wired and why they can cause issues: http://www.classiccougargarage.net/showthread.php?tid=86

I have been converting tachs and making OEM style tachs for cars that did not have a tach since 2005. My tach conversions come with a lifetime warranty and are so good that another shop asked me to do conversions for him, then disassembled them and tried to buy my custom parts from the vendor using my part numbers!

I stand behind all of my products and if you are considering a three wire conversion I hope you will look at my offerings before choosing a vendor.

My website: http://www.rccinnovations.com
That's awful that someone tried to reverse engineer your work - it really just shows how pervasive greed is in the world.

I've also got the RCCI (Rocketman's Classic Cougar Innovations) modified tach in my '71. I ran without a tach for many years (almost 10 years, actually) until I realized that I could simply have my stock tach upgraded with modern electronics. Works great and it is also DEAD ACCURATE, I've verified this using the 36-1 trigger wheel and the crank position sensor. Love the fact that the appearance is stock as I was seriously considering doing a wholesale replacement of the gauges with aftermarket units. I also have had my fuel gauge recalibrated and it reads accurately once again. ::beer::
I can personally attest to the high level of customer service the Rocketman provides. He went above and beyond to help me resolve an issue I was having. The best customer service experience I have ever had with any product.

 
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