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Tach and 3 wire
#1
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.
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#2
Here is a good article that explains the three wire set-up:
http://www.classic-cougar.com/images/sto...ctions.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.

2013 Ford Focus SE Flex Fuel 5spd - Daily Driver
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#3
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/showt...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

Bob

Tachs, Voltmeters, Headlight kits, Wiper delays and more at
[Image: smlogo.jpg]
Rocketman's Classic Cougar (and Mustang) Innovations, LLC
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#4
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 won't 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.

Kevin

1971 Mach 1
408C Stroker
C4 w/3,000 stall
8.8" Rear w/3.73's
Disc brakes all way around.

[Image: 28ivsix.png]




                                                                                             
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#5
I highly recommend him as well. He did a 71-73 Tach and '68 ammeter for me, and am happy with both.

Steve
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#6
TheRktmn;158650 Wrote: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/showt...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.
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#7
Hi
I bought the 3 wire gauge too. What will happen with the stock coil sensor wire? Or is it for an other gauge?
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#8
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.

Bob

Tachs, Voltmeters, Headlight kits, Wiper delays and more at
[Image: smlogo.jpg]
Rocketman's Classic Cougar (and Mustang) Innovations, LLC
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#9
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.

'Mike'
73 Convertible - 351C/4V CC heads/4bolt/forged flat tops/comp 270/rhodes/mallory unilite/tri-power/hookers/glasspacks/c6/3.50 limited slip/Gear Vendors/Global West sub frames, strut rods and shelby style traction bars/ Rear sway bar/tilt steering (not original)

Pics of modifications included in:
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#10
My next purchase will be this tachometer from Rocketman, to replace the idiot light Smile
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