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Replaced alternator and now headlights flicker slightly

Discussion in 'Intermediate CJ-5/6/7/8' started by John_pro2a, Jul 18, 2007.

  1. Jul 18, 2007
    John_pro2a

    John_pro2a Member

    Joined:
    Nov 25, 2006
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    75 CJ:

    Last week it wouldn't start. Figured out it was the alternator. So charged the battery (red top), replaced the alternator and now seems to be working ok.

    Headlights are brighter than they've been since I got this thing running, so I'm guessing the alternator hadn't been working right for a while.

    Anyways... now the headlights flicker ever so slightly. The flicker is not super noticable, but if you look for it you'll see it. Seemingly it keeps time with the idle... If I give it a little gas, the flicker speeds up.

    I don't think it used to do this (I never noticed a flicker before).

    So, what could it be? Should I be worried? Something to track down, or ignore it?

    Things done or replaced recently that have to do with electrical: full tune (wires, plugs, points), new coil, new alternator, new voltage regulator, new electronic control modual, new turn signal switch.
     
    John_pro2a, Jul 18, 2007
    #1
  2. Jul 18, 2007
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

    Medford Mass USA
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    I would suspect that you have a high resistance circuit (bad ground?) somewhere in the headlight circuit, and you're seeing the voltage fluctuate with the alternator speed. If you add relays on the fender well, going directly to the positive battery cable via the starter solenoid, you will make a low resistance path to the lights. This should make your lights maximally bright all the time, and decouple them from the alternator output. I'd check the light grounds first though.
     
    timgr, Jul 18, 2007
    #2
  3. Jul 18, 2007
    Howard Eisenhauer

    Howard Eisenhauer Administrator Staff Member

    Tantallon, Nova...
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    Nov 22, 2003
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    :?

    Not so sure I'd agree with that Tim-

    Consider that he reports that the lights are now "brighter than ever". That doesn't seem like an indication of a resistance in the light circuit.

    My take is that the lights are flickering at constant engine RPM, as the engine speed increases the flicker speed increases. Due to thermal lag in incandescant lights & the eye's tendency to see anything faster than 50 or 60 cycles per second as a constant light I'd think that the alternator output is actually varying at a noticeable rate.

    Now, this is how alternators work - the regulator is switching the field windings on & off with a duty cycle that averages out the output voltage to the preferred charging level but this generally happens so fast, hundreds if not thousands of times a second, you'll never notice it.

    Since it is noticeable my first guess is that the regulator is snaffued, switching on & off at way too low a rate. This may also be the reason for the brighter lights.

    Second guess is that theres some blown diodes on two of the three winding outputs, so theres a noticeable AC component to the output but its too late at night for me to figure out how slow the engine would be turning for you to actually see the flicker :)coffee: ?)

    Third guess is that the new alt requires a different wiring setup than the old one, say going from a one wire alt to one that needs an input to the reference terminal.

    I'd get a voltmeter & check the alt output for DC & AC voltage levels. If you can find an old pair of high impedance earphones (2-3 thousand ohms, NOT the kind that came with your IPOD :shock:) you can run them between the alternator output & ground. If the regulator is working properly you'll here a buzz, if its bad or the diodes are screwed you'll probably here a clicking noise in time with the lights flickering.

    H.
     
    Last edited: Jul 18, 2007
    Howard Eisenhauer, Jul 18, 2007
    #3
  4. Jul 19, 2007
    John Strenk

    John Strenk Member

    Shalersville, Ohio
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    Nov 28, 2006
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    112
    Yeah, the fact that the flickering increase with speed caught my eve and is a problem.

    Just turn any AM radio on and see if you hear a lot of growling static and then disconnect the alternator and listen again.

    What would happen with a poor ground between the case of the alternator and ground? Would that raise the voltage the battery will see and the electrical system as a whole? The regulator might be internal to the alternator but is arcing throught the poor ground causing the flicker. Naahh that arcing would be to random unles there is some mechanical reason for it improving.
     
    John Strenk, Jul 19, 2007
    #4
  5. Jul 19, 2007
    NorCoJeeper

    NorCoJeeper Member

    Ft. Collins CO
    Joined:
    Feb 10, 2006
    Messages:
    470
    'Nother vote for blown rectifier diodes as a first check. Any FLAPS can check the alternator, especially the one who sold it to you :) You'll be looking for ripple which should be very low, less than 1/4volt IIRC.
     
    NorCoJeeper, Jul 19, 2007
    #5
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