Tach not working

[smallblock289]

Hi ,
     Can anybody give some help with my tach , I used to own 67 GT500 1926 but now I,m running 67 GT350 1789. The problem I have is I have had the car off the road for 5 years  , thought I would give the motor and tranny a rebuild within a couple of months but things never work out that way. The car has had to be completely rebuilt due to the past history of it .The original dash was missing along with most everything else so I fitted a new dash with 140 speedo and 8k tach all was working fine until i pulled and rebuilt the motor .The tach was a three wire unit not the original 2 wire. now all connected up as before but the tach will not work sometimes it will pulse up maybe 2-300 revs . The only thing i have changed from before is i have fitted a 289 hi-po dual point distributor , could this be where my problem is with having 2 sets of points is it picking up a wrong signal and if so how do i fix it. Any help would greatly be accepted

[The Going Thing]

Do you still have points, or are you running an electronic replacement?

[smallblock289]

Hi,
    Thanks for the reply I,m running dual points not an electronic system.

[shelbydoug]

The tach wiring is simple. One wire comes from the main power lead to the tach, the other wire goes to the coil.

The factory ran it in series but that could keep the car from starting if the tach fails.
Best to run a wire separately from the tach to the coil.

Even though most often the coil connection is suspected, I find that it is the power to the tach under the dash that has come loose.

This becomes even more common if you just did an ignition swith or directional switch replacement.

Go back and double check, your double checked crimped connections. You likely missed something.

[roddster]

  I'm mystifed over the "three wire tach".  What?  Just two wires on the factory ones I have, plus a snap in light.

[Coralsnake]

Its been modified by one of those guys thats smarter than a Ford engineer

[shelbydoug]

Its been modified by one of those guys thats smarter than a Ford engineer

The modification was from a Ford Technical Service Bulletin which as you know was run by a GM subversives.

Although looking at the work that Kar Kraft did for Ford, I sometimes question the competency of the original Ford Engineering staff. The must have actually heard of electricity at some point?

[The Going Thing]

I hope it wasn't Tachman that did your three wire conversion.  I'm sure it will tell you on the back of the tach. He's proud. Bob AKA Rocketman does them and I am sure he'd be glad to walk you through the testing and repair if necessary. The link is below.

I had to have Phil Severence of Phildon restorations fix Tachman's mess with my tach and speedometer. 
Below is the contact information for Rocketman.  He's well known. He restored my clock and also I purchased his relay package for the headlamps. It makes a world of difference even with halogen lamps.



http://www.rccinnovations.com/index.php?show=menu-mustang-all

[roddster]

  And the Ford Tech Service bulletin number is __________?

[shelbydoug]

  And the Ford Tech Service bulletin number is __________?

...don't remember.

[The Going Thing]

Rodster- There are almost NO replacement parts for our original tachs. Many are opting for the replacement tach drive that uses a modern three-wire drive instead of the old current sensing units our cars came with that are so problematic with any modern electronic ignition conversion.
Phil Severence is the only one I know with NOS parts for them. He fixed Tachman's mess after he refused to fix it.
The feed for the Pertronix Ignitor II required me to pull off the red BEFORE the tach from the right. Scotchlok five feet of 14GA wire, pull it through the ignition/engine feed boot with a hanger or a fish and run it to the positive (red) wire from the ignitor. Either solder it and shrink tube or get a bullet connector and crimp. ( I like the bullet connector) You can remove the distributor from the car if need be.
The black wire from the module has a terminal. tighten it up with the nut and slide the factory wiring on the correct coil terminals.
It's that simple. Everyone over-complicates the 12V direct feed for Pertronix. Others whine and call them junk because they don't read and wire them correctly. 12V means 12V. Not 6-8V. The Pertronix II and coil has been in my car since about 2006. There's nothing wrong with them.
However, leave your key on with points and see what happens...  Well, just go by points and a condenser and be done with it.

[67 GT350]

Does that mean that if the tach malfunctions, the car will not run?

[Bob Gaines]

Does that mean that if the tach malfunctions, the car will not run?

Typically on the inline circuit tachs. In that case you have to disconnect the tach and plug the two ford harness ends (male and female) into each other bypassing the tach circuit to get power to the coil. Short term fix to get you going is to hot wire but that will eventually burn out your coil and in rare occasions cause it to explode after it gets too hot from the extra juice.

[The Going Thing]

If you have a Pertronix that isn't an issue. Yes, the car won't run with a tach failure. It completes the circuit. The three wire conversion eliminates this concern as well.