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Thread: FLICKERING LIGHTS-need a little help here

  1. #1
    Join Date
    Apr 2009
    Posts
    2

    Default FLICKERING LIGHTS-need a little help here

    Need some quick help with my flickering lights problem. Running lights at night - lights quickly pulsate from a full bright to a dim (repeated back and forth cycle about twice per second) and the charging gauge needle on the dash bounces back and forth as well. What might this be? Alternator problem? It looks fairly new just a little dirty with some oily dirt on it.

    Belts were tightened yesterday but that didn't help. Fairly new battery and cable on the truck. I also have a new HO alternator. Should I install that to see if it goes away? At least I could rule out ALT vs wiring?

    Any help would be appreciated. If anyone could provide a short list of "THING TO DO" that would be great!

    TIA.

    Jeff in Wilmington, NC

  2. #2
    Join Date
    Feb 2009
    Location
    Aiken, SC
    Posts
    2,423

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    This problem is usually caused by bad grounds. Check the negative battery cable, the ground at the alternator, and the grounding screws at the voltage regulator. Check the positive battery cable as well.

    More rarely, a defective battery will cause this, but you'd already know about that from having had to jump start the vehicle all the time.
    Allan E.
    Curmudgeon Extraordinaire
    Charter Member, Old Hippie IH Club
    Old fashioned binder freak

  3. #3
    Join Date
    Apr 2009
    Location
    Rock Island TN.
    Posts
    31

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    I have encountered such a problem on a "off brand" vehicle twice before and the alternator was the culprit once and the battery the second time. I would shoot for the Alternator. Later, Paul
    Black Smoke Customs is now open in Rock Island, Tennessee. We are addicted to International's and Cummins B series motors. The only thing we don't do is paint and body,,,yet.
    We support ASE Certification.

  4. #4
    Join Date
    Mar 2009
    Location
    California
    Posts
    110

    Default

    Which vehicle is this, and do you have the older mechanical regulator, or the electronic style? Also, by "running lights" do you mean the headlights, tail lights and side markers, or just part of these?
    Will this flickering occur when the engine is off too, or just when it's running, and if the latter, are the headlights dim when the engine isn't running? That would indicate either a bad battery or a poor connection between these items.

    The more detail you can provide, the better the analysis another can do for you.
    Sounds as if Allan E. has some of this info. so his suggestion is probably a better starting place. Right now, I'd just be guessing.

  5. #5
    Join Date
    Feb 2009
    Location
    Aiken, SC
    Posts
    2,423

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    The pulsing you see is the regulator turning the alternator off and on. The reason it does so is that it "sees" a low voltage when the alternator is on, and it "sees" a high voltage when the alternator is off.

    Start with the "alternator is off" situation. Inadequate voltage at the sense wire is about to turn the alternator back on, but why?

    The short reason is that there is so much current coming out of the battery that it bogs down the voltage. This can be caused only by too much resistance in the circuit, such as:
    a bad battery cable
    lack of a good ground from engine to frame/body
    bad regulator
    bad sense wire to the regulator

    It can be caused by a bad alternator, but as a general rule, if this vehicle has an external regulator, such is as found on most IH light line products, that will not be the case. It is a common symptom of 1 wire alternators because the regulator is built in to the alternator.

    If this is some other type of vehicle, or has been converted to a 1-wire alternator, I'm with Paul. Otherwise, I'd go with the grounds to the regulator first, then the regulator itself.
    Allan E.
    Curmudgeon Extraordinaire
    Charter Member, Old Hippie IH Club
    Old fashioned binder freak

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