Factory Tach Help 70 RS Z

Discussion in 'Troubleshooting & Diagnosis' started by bgreene30, Oct 17, 2017.

  1. bgreene30

    bgreene30 Member

    59
    0
    Aug 11, 2011
    Orange County, CA
    Hi. From what I can tell, there is a brown wire that runs the factory tach. Mine does not work. When we run the brown wire to a 69 el Camino with factory tach it works. When I run his wire to mine it does. It work. Both my distributor and his are HEI.

    Any troubleshooting ideas to determine if it's the printed circuit board or tach?

    Does anyone have an hei powering the 70 tach? Wondering if maybe it's the hei causing the issue?

    Help
     
  2. hogg

    hogg Veteran Member

    3,081
    24
    Dec 29, 2000
    pegram,tn.,cheatam
    check ground side and hot wire,i run the same ,works fine
     
  3. bgreene30

    bgreene30 Member

    59
    0
    Aug 11, 2011
    Orange County, CA
    On the tach? Hits good, where should it ground?
     
  4. tom3

    tom3 Veteran Member

    10,627
    41
    Aug 1, 1999
    ohio
    I have the original tach in mine with an HEI dizzy, works fine. I read somewhere years ago that there are two types of tach systems, one with a negative pulse, one with positive. I'd suspect a mismatch with yours assuming everything else is right. Sorry I can't help more.
     
  5. hogg

    hogg Veteran Member

    3,081
    24
    Dec 29, 2000
    pegram,tn.,cheatam
    the ground is the metal part of cluster , fuel gauge dash ground,i thank and then there is a hot ,+ stamped and stud on metal backing plate of tac where the hot wire,part of back of cluster is,, i thank,, if you got a meter you can check for voltage at 12v stud and for ground on the backing plate of tac. maybe
     

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