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Tach not working
#1
When I purchased this 73 Mach the tach wasn't working. All other gauges working. Trying to figure out where to start. It does have a pertronix I device under the distrbutor. All wires seem to be in place. Its a matter of tracing the wire back thru the firewall and see where it goes. What else can I check or do some wire from point a to point b to see if the tach is working at all. Please advise with text and pictures.
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#2
http://www.7173mustangs.com/thread-weak-tach-signal
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#3
I have no MSD products installed. Basic coil. Does the petronix still have an effect on the tach. It also looks like the wire going to the tach is coming off the positive side of the coil. Please advise.
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#4
Does the engine start and run even though the tach is not reading anything?

the tach is wired in series with the positive side of the coil Red/Green wire. so that is correct.

Now the tach can fail 2 ways, if the tach completely goes out the engine will not fire, because no power will get to the coil. the second will be failure in the spring or magnet for the needle. the needle is pressed on to a sleeve and can fall off and give the appearance of the tach not working. or the internals could of died for the gauge.

you can bypass the tach in the event of failure by jumping the connector behind the dash for the tach.

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ignition modules. If your using a petronix III ignitor your tach will not work, it produces a different tach signal then earlier versions the petronix I, and II modules work with the factory ford tach.

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if the engine is running, and your using a Petronixs I or II ignitor system and the tach isn't working.

you can try pulling the tach connector behind the dash and making sure the engine will not fire. this will tell you
the tach is working but not showing RPMS. in this case you will need to replace the tach in the dashboard with a new one.

you can also check voltage on the connector and see if you get 12 volt readings on it from the coil.

i'm not sure if anyone offers a tach restoration so you may need to hit auction sites to find a replacement.



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#5
The engine still runs fine without the tach moving.
I will try you troubleshooting methods thanks.
You are right. It seems no one has a replacement tach for the 71-73 Machs.
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#6
aftermarket tachs can be used but you may need to add wires to the coil and add a jumper to bypass the oem tach
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#7
I checked with Tachman last year to see if he rebuilds our tachs....won't even touch them. I did talk another place on the phone and he said that he will rebuild the factory tach with new internals.....just means that you have to run a new wire out to the coil and distributor as it will be wired up like a new tach.

here's the link for his site
http://www.autoinstruments.com

[Image: 1_14_01_12_10_54_29.png]

Ken

73 Convertible 302-4v-3spd yellow /white int

08 Bullitt 4.6-5 spd black/black int


All I ask is a chance to prove that money can't make me happy
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#8
thanks for the tip. I'll look at running a new wire just to see if the tach works at all.
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#9
sgtjd;24183 Wrote:thanks for the tip. I'll look at running a new wire just to see if the tach works at all.


I don't think that will work....because if you run wires from the tach itself to the coil and distributor, you will bypass the resistance wire.....and the car won't start.... you need to close the loop by completing the circuit. I think that there is a diagram of the tach hookup under the data tab at the top of the page.

[Image: 1_14_01_12_10_54_29.png]

Ken

73 Convertible 302-4v-3spd yellow /white int

08 Bullitt 4.6-5 spd black/black int


All I ask is a chance to prove that money can't make me happy
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#10
if it was me i would hit ebay, get another tach, plug it in see it it works, take apart the instrument cluster , rebuild everything while i was inside, throw a new regulator and circuit board on it and call it fixed.

otherwise your going to spend more money hack apart your dash, splice wires and run new wires all over the place.
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