Question about 1992 Mercury Grand Marquis

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My speedometer is digital. When I turn on the headlights the dash lights go dim and I can hardly see my speed. Even when I have the intensity knob turned all the way.I have had a new light switch installed and it did not fix. Also on a bright sunny day I can not see my speed digets. My mechanic says that the bulb is okay.

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  • maxeetay Mar 21, 2011

    No, the digets are green

  • maxeetay Mar 21, 2011

    no , the digets are green

  • maxeetay Mar 21, 2011

    I tried to answer you, but I am not sure that it went through.

    The speedometer digets and other digets are green. It isn't the digets that

    are dim , it is the backgrounnd light. I can not adjust them.

  • maxeetay Mar 21, 2011

    I have digetal speedometer (green). The background light dims when I turn on my headlights until I can hardly read the speed I am going. The intensity know does not make it
    brighter but will make it completely dark. I have had a new light switch put on and the mechanic says it is not the bulb. Can you give
    me some information. Thanks

  • maxeetay Mar 21, 2011

    Thank you, I will take this information to my mechanic.



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Ok, when you turn on the head lights the dash lights get dim.But if you turn off the dash light does the dash light gets bright again or it remains dim.------ If the dash light becomes bright as you turn off the head lights then its a short in between dash lights wirings and headlight wirings.There is a confirm short.rte check the head light switch wirings and dash light wirings.Any of the wirings is getting in contact with metal part or ground wire is getting loose or its getting connected to any other live wire. ------------- Also check the battery voltage.And battery to alternator wiring and connections.Get the battery and alternator voltage checked separately.---------If the battery or alternator voltage is low then, this low voltage can be the issue.Also check the dimmer switch.Remove and reconnect dimmer switch. ---------- Check out this possibilities.This should help.Thanks.Helpmech.

Posted on Mar 21, 2011

  • raj somaiya Mar 21, 2011

    Ok.That should help.Keep updated with the results.Thanks.Helpmech.


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Is it the blue led digits its possible the led is on its last legs

Posted on Mar 21, 2011

  • Robert Charpentier
    Robert Charpentier Mar 22, 2011

    Cluster Dimming


    Cluster dimming is controlled by the interior lamps dimmer (rheostat) in the headlamp switch through Circuit 19.

    Quick Check

    • If cluster does not follow the dimming of the other interior lamps, check that proper rheostat voltage is present at cluster inputs.
    • If all interior lighting is affected, check continuity of circuit from the headlamp switch to the fuse.



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