Tach bounce

Discussion in 'Troubleshooting & Diagnosis' started by CoastieJoe, Dec 22, 2017.

  1. CoastieJoe

    CoastieJoe New Member

    Jul 29, 2017
    I have a 74 Z28 with a 70 LT1 powering it. For awhile now the tach has been bouncy. It seemed like bumps in the road caused it to bounce at first but then it randomly jumps quite a bit when your get it throttle. To add to it recently Ive noticed on start up it goes crazy at idle unless I press in the slack on my clutch which also brightens the interior lights. I don't know if this all stems from the same problem. Help!
  2. Gary S

    Gary S Administrator Lifetime Gold Member

    Apr 14, 1999
    Bismarck, North Dakota
    It sounds like you have some kind of wiring issue. However, the first thing I would try for the lights is to spray a bit of contact cleaner into the light switch. To be on the safe side, disconnect the battery first and let it dry out some before putting power back on. Sometimes the rheostat inside the light switch for dimming the interior lights gets dirty and causes lighting issues.
    The tach issue could be separate, or if you have a bad wire or connection in the dash, the voltage to the dash could be dropping. That would cause multiple issues like the tach and the lights too. A voltage problem could be caused by either the power wires to the dash or the ground wires to the dash.

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