After I rebuilt my 351w and put everything back together, i noticed the tachometer wasn't working. Does anyone know where the tachometer wire is under the hood and how i can test it without opening my dash? I know it worked before the engine rebuild. Thanks
Goes to the negative side of your coil. Not the best diagram for what you are doing but here is a diagram showing the engine gauge feed harness at the bottom of the page.
http://1970mgr.org/_AddTachCluster.htm
Tachometer is wired like this, hopefully I can be clear. There are only two wires, one into the tach and one out.
1. Wire from ignition switch into tachometer provides the switched 12V power.
2. Wire coming out of the tachometer goes through a resistor wire then to the positive side of the coil.
That's it. Very possible the tachometer simply reached the end of its life.
If you car runs and the tach doesn't work, there is a good chance something in the movement is bad. New parts for the movement are not being made. If you're lucky a transistor or capacitor or resistor on the small circuit board is bad. But, usually the movement goes bad or sticks from wear and cannot be repaired.
These early Ford tacks are known as "Current Triggered Tachometers" as opposed to "Voltage Triggered Tachometers. Most everybody has the factory tachometer retrofit with new modern day internals which converts it to a "Voltage Triggered Tachometer" and using 3-wires to connect instead of two (one is a ground). It can then be used with modern day electronic ignition systems or your existing points system. I would go to Rocketman's Classic Cougar Innovations,
http://rccinnovations.com/index.php?show=menu-tach-all or Redline Gauge Works,
http://redlinegaugeworks.com/ . There is also the Tachman. Go to him if your in the mood to be chewed out if you call at the wrong time or ask too many questions.
If you remove the tachometer, you need to install a jumper wire across the two terminals on the tachometer harness connector so your engine will run. With that in mind, you can probably determine the factory tachometer can and often fail in a manner that will prevent the engine from running.
Sorry, I didn't have more positive news this time.
Regards,
Mike