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  • Electronic tach wiring

    I'm helping a friend install refurbished instruments in his dash ('74 model). (Unfortunately, I was not involved in helping remove them). I am baffled by the electronic tach because my car has a mechanical tach. The refurbished electronic tach has two wires, red and white. It grounds through the case of the instrument. The instructions say to wire the white wire to the "tach sending wire" or the "distributor side of the coil." The instructions say to wire the red wire to "IGN." We thought we had done this correctly, but after installation the car wouldn't start. We disconnected the white wire to the tach and the car started. Can anybody help? I have a Master's book and schematics, but those references are for mechanical tachs.
    Wouldn't "IGN" be a white wire on a '74?
    Thanks for your help!
    1976 Pimento/black
    VTO alloy "Minilites"
    Dolly Parton's removed
    Carbs by Poolboy

  • #2
    The IGN wire is probably the white wire that feeds the fuse for the green wires circuits....that's probably where they want the red tach wire connected to.
    The tach's white wire must go to the coil's negative terminal...That would be the same terminal that has a wire going to the rim of the distributor.
    Is the tach illuminated ? There should be some method of lighting up it's dial, right ?
    BTW...I'm not responsible for smoke or blown fuses....
    Driving a 1973 TR6
    Doing ZS carb repairs
    email kencorsaw"at"aol.com

    Comment


    • #3
      Dear Ken,
      Ha, your disclaimer made me laugh. That's the same thing I told the car's owner!
      Looking at the Master's book, I came to the same conclusion that you advised. I connected the red wire marked "IGN" to the white wire of the Ignition dash light. There was a small white wire with purple stripe coming from the coil to the vicinity of the tach, and it was unattached to anything. We connected that to the white wire of the tach and the car wouldn't start...no spark. When we disconnected it the car started normally, but obviously we had no tach reading.

      I've got a call into the instrument manufacturer and see if they have any further advice about where the white wire connects.

      And yes, the bear of the whole project was connecting all the new instrument LED lights to the old wiring harness red/white wires. The LED are glued to the instruments, which I don't like. It's going to be a real booger if there is ever a problem with any of them. They all lit and all the instruments worked properly except for the tach. We'll get to the bottom of it.

      Thanks for your reply!
      Ron
      1976 Pimento/black
      VTO alloy "Minilites"
      Dolly Parton's removed
      Carbs by Poolboy

      Comment


      • #4
        A couple things stuck me in that last post, Ron.
        The tach's red wire should not have been connected to the "Ignition dash light".....The best place would have been to the vacant terminal on the fuse box with the white wire feeding the fuse for the green wire circuit....on the white wire side of the fuse...not the green wire side of the fuse.
        And that dangling white wire with the purple stripe is supposed to be the wire from the oil pressure switch to the Anti Run-on Valve....I can't think of any use for it other than it's intended use.
        The tach's white wire needs to share the terminal on the coil with the wire from the rim of the distributor.
        Try that.
        Driving a 1973 TR6
        Doing ZS carb repairs
        email kencorsaw"at"aol.com

        Comment


        • #5
          Dear Ken,
          Hmmm. Now you've got me thinking in the right direction. This car has been touched by so many people that it has some strange gremlins. For example, it has no Oil Pressure sending unit or Anti run-on Valve. The white w/purple isn't part of the wiring harness, it's an add on that I think came with the electronic ignition. At any rate, you've got me on the right path. I'll go "red wire to the white side of the fuse box" and "white wire to the distributor side of the coil." And, if there's no smoke, I'll let you know.
          Thanks again for your replies.
          Ron
          1976 Pimento/black
          VTO alloy "Minilites"
          Dolly Parton's removed
          Carbs by Poolboy

          Comment


          • #6
            Dear Ken,
            Well, you were exactly right. Tach is now working properly. The problem was the white wire coming off the tach...it needs to go to the distributer side of the coil. The red wire just needs switched positive 12V, which the previous owner had gotten off the white wire that illuminates the ignition dash light in the tachometer. He did this via a blue plastic wire splice like the ones in a boat trailer. I removed that and ran a new red wire thru the firewall to the vacant spade underneath the white wire on the fusebox, as you suggested. This is much cleaner and safer. I hate those boat trailer "squeeze splices." So, problem solved with no smoke or blown fuses!
            Thank you for your help,
            Ron
            1976 Pimento/black
            VTO alloy "Minilites"
            Dolly Parton's removed
            Carbs by Poolboy

            Comment

            Electronic tach wiring

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