Question about 2005 Mercury Grand Marquis

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Head lights turn off in darkness even if on manuel. Wait a bit and they come back on. I replaced the headlight switch but it didn't take care of it.

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  • foxphoto46 Oct 03, 2009

    I don't feel like that is the solution because I'm driving at night and the headlights are on and then for no reason, I think I hear a click and they are off. I pull off the road and the lights are still off. I turn off the ignition, sit there for about five to ten minutes, restart the car and they are back on. Nothing moved. Could it be a light sensor? I try them on "Auto" and manual and it doesn't make a difference.



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Its not the headlight switch, but a loose connection of the main wiring of the Light that gets loose due to vibration and again comes back when another **** or bump and the lights are back. I would recommend that you get this cicuits examined by a PC at any garage or service station which will be able to pinpoint the distance from where it loose .... sodeep

Posted on Oct 03, 2009

  • Sudeep Chatterjee
    Sudeep Chatterjee Oct 04, 2009

    If you are sure that you do hear a click before the lights go of, then the click sound is from the relay. The dynamo is producing higher current than its rating. Since its night time & your headlights are on(Halogen or high power) it consumes power from the dynamo and the excess current, after giving power to the electrical equipment and also to the rectifier for recharging the battery. As soon as the battery gets charged a time will come that no more charging of the batteryis required,i.e. fully charged Now the current being used by the dynamo is much more than whats required and this extra current will be passed on to the headlights. For protection of the headlights is a relay which trips as more curremt is passing thru it. It will start getting heated until it triggers the relay for the lights by switching it off. As you wait it will cool down so that the relay is at on position. Cranking/starting the engine requires a good amount of current to the starter, Thus some charge from the battery has been used up. Now again when you start off, the same cycle repeats, resulting in headlights getting switched off.
    Have the output of the dynamo corrected and this problem will automatically be rectified.......sodeep



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