Tachometer is acting up.

Lincoln Mark VII

  1. Elessee

    Elessee Well-Known LVC Member

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    1988 LSC. My tach works fine unless I turn on the headlights.

    With headlights on, the tachometer lamp is dark. The rest of the dash is illuminated as normal.
    Also, with the headlights are on, the tach itself doesn't function. The dial indicator stays on zero.
    Everything else works.
    Turn off headlights and it works again.

    I have a feeling there's a problem with the headlight switch, and it may need replacing. But I'm hoping someone has another solution, like a loose wire. I'm far away from home, no shop manuals, no tools. Replacing the switch would be very difficult.

    It happened suddenly last week. Nothing was changed, no recent work was done on the car and there are no other problems.
    Thanks for any ideas...
     
  2. Elessee

    Elessee Well-Known LVC Member

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    UN-fortunately, the problem fixed itself. I hate when that happens because it's not fixed.
    (Additional symptom: Didn't notice it before but the fuel gauge was maxed out when the headlamps were on, and the tach was dead.)

    I was messing with the dash brightness dial next to the headlamp switch. It is some sort of resistor, probably a slider, adding or subtracting resistance to dim or brighten the dash lights.

    At night, the dash lights have been too dim lately (280K miles) and I've considered shooting a little WD40 into the crack.
    Anyway, there might be a fault in that circuit which caused the tach / headlight problem, and messing with the dial fixed it.
     
  3. joegr

    joegr Dedicated LVC Member

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    Loose ground to the dash cluster?
     
  4. Elessee

    Elessee Well-Known LVC Member

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    Thanks. That's worth checking out. Grounding... Yeah.
    I recently added an engine ground because hot re-starts were very hard on the starter motor. Slow grind. The internet suggested poor engine block grounding. An additional ground strap direct (short battery cable) from the alternator to the body worked wonders.
    I'm still on the road. Logged in here because another problem.
    Yesterday, my passenger door window slowly closed. Then it dies (completely closed, thankfully) and I was just gonna check the fuses.
    I will also check for good grounding wires under the dash.. whatever I'm able to see...
     
  5. OldSchool1

    OldSchool1 Dedicated LVC Member

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  6. Elessee

    Elessee Well-Known LVC Member

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    "2) Window motor. They're easy to do and normally last a decade."

    I've replaced the driver-door motor, and agree. It's easy once you've experienced it.
     
  7. Kcz5o

    Kcz5o New LVC Member

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    This reply might be late but I recently bought an 89 LSC
    . My tack would work fine until I turned on the headlights and then it would quit. If I turned the headlights off the tach would then work again. I took out the instrument cluster and cleaned the connections and his has worked since then.
     
  8. Elessee

    Elessee Well-Known LVC Member

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    I agree the problem is a poor connection somewhere in the instrument cluster.
    But I'm on the road, and have no place to work, and no tools. Just spinning the dimmer wheel several times, back and forth, seemed to clean the contacts, and cured the tach problem, temporarily.
    I think it's the dimmer. Even at max, my cluster lights are dim. A new headlamp switch might fix that too. Perhaps a few of the lamp circuits (and the tach, and the fuel gauge) ground wires pass through that dimmer.
     

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