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Aftermarket Tachometer Hook-Up

Discussion in '1969-1972 K5 Blazer | Truck | Suburban' started by cleszkie, Sep 27, 2002.

  1. cleszkie

    cleszkie 1/2 ton status

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    I hate to even ask this, but I am having a problem with getting my aftermarket tach to work properly on my 72 K5. I run a 350 SBC with a Mallory Unilite distributor, and Holley Pro-Jection 2D system. I've contacted both Mallory and Holley tech departments to see if I need to use some sort of capacitor/resistor off of the negative coil terminal to "condition" the signal so the tach works. They both said that their systems do not affect the factory tach wiring. I also have tried about 3 different tachs with the same results. My question is how is the factory tach wired in? I have always assumed black to ground, red to switched 12V source, green to negative coil terminal (for inductive style distributor), and white to dimmer switch. Any help on this would be mucho appreciated.
     
  2. Michael

    Michael 1/2 ton status

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    It looks to me like the Unilite is just an optical firing distributor going to a standard or hipower coil. The aftermarket tach should work off the negative side of the coil, but I'm guessing you've already attempted that. I'm not sure on the OEM tach wiring, but what you said seems correct. You might try connecting the tach with new seperate wires and not use anything that is on the truck now. Good luck!
     
  3. chulisohombre

    chulisohombre 1/2 ton status

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    thats the same way i hooked mine up before i put the msd ignition back on.after i hooked up the msd the tack would not work.it had to be connected to the msd box itself to work correcty.
     
  4. cleszkie

    cleszkie 1/2 ton status

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    It turned out that my externally regulated alternator was the culprit. I wired in an internally regulated alternator and all problems went away with the tach and everything else electric.
     

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