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Idiot lite on 1965 CJ5

Discussion in 'Early CJ5 and CJ6 Tech' started by Greevesman, Mar 3, 2015.

  1. Mar 3, 2015
    Greevesman

    Greevesman Member

    Napa, Ca
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    I bought a 1965 CJ-5, un-molested/original. The Idiot lite was not coming on so I assumed incorrectly the battery was getting charged. I did not run at nite so the only load was starting. I got down in a canyon and shut it off and it wouldn't start. Had to be rescued.
    Wondered why the idiot lit didn't warn me about lick of charge. Found where the wire at the voltage regulator had been disconnected either because PO couldn't figure out to make it work or he didn't want me to know about the non working generator.
    From the wiring diagram for CJ5s after a certain serial number, it looks like both idiot lights come off the same terminal on the ignition switch. (Oil lite works fine), then thru the bulb in the instrument cluster, then to the BAT terminal on the voltage regulator. I traced the wire back to the socket and there was continunity and a good bulb. Connected everything up and with the key off and engine not running, the idiot lite was on. Click the key to "on" but did not start the engine and the lite is off. Not sure how the idiot lite works but maybe, since both sides of the bulb are on positive side of the battery, the bulb "compares" current on either side of it's location. If there is a delta voltace(current?) it lites up?
    Not sure what is happening here and would appreciate any tips/intellegence.
     
  2. Mar 4, 2015
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

    Medford Mass USA
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    This is correct. There has to be a difference in potential (voltage) across the bulb for current to flow. No delta, no light.

    Starting with the key on and the engine stopped, the alternator field is at ground potential, current flows and the light is on. When the engine starts, the field self-energizes and the ignition and field are both at 12V level. No current flows through the bulb and the bulb is not lit. The job of the regulator is to adjust the current in the field so that the generated current (full wave rectified three-phase AC, for an alternator) charges the battery and matches the load, as needed.
     
  3. Mar 4, 2015
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

    Medford Mass USA
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    This is the Delco SI alternator, but the Motorola alternator operates similarly, except that the regulator is outside the alternator case.

    [​IMG]

    To change how much output the alternator has, the regulator changes the current (and by ohms law, voltage) through the field. The central part is that zener diode at the middle of the circuit. That's the voltage reference that the alternator works off of. The field wire from the switch only gets things going at start-up. Residual magnetism in the field is enough to self-energize once the engine speed is high enough, so if the bulb burns out, the alternator will still charge the battery in normal use.
     
  4. Mar 4, 2015
    Howard Eisenhauer

    Howard Eisenhauer Administrator Staff Member

    Tantallon, Nova...
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    Alternator or generator?

    If a genny the light should actually go to the "armature" terminal of the regulator.

    H.
     
  5. Mar 4, 2015
    Greevesman

    Greevesman Member

    Napa, Ca
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    Stock 65 with a brand new generator and regulator. The wiring diagram shows both the oil pressure and charging lites coming off the same terminal on the ignition switch then thru the lite witch is an isolated socket, un grounded. then the wire appears to go to the BAT terminal on the regulator. This results in key off, engine not running, lite on. Key on, engine not running, lite off. Something is not right. Anyone have a correct wiring diagram? Wiring harness has not been modified. (I think) Original regulator is Autolight. System is now charging the battery OK.
     
  6. Mar 4, 2015
    Walt Couch

    Walt Couch sidehill Cordele, Ga. 2024 Sponsor 2023 Sponsor 2022 Sponsor

    cordele, Ga.
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    Well Howard E. gave you the answer. Move the Gen wire (idiot light) at the regulator, to the (A) terminal or Armature terminal. If your regulator has a (I) terminal for Ignition then the idiot light wire will go there.
     
  7. Mar 4, 2015
    Howard Eisenhauer

    Howard Eisenhauer Administrator Staff Member

    Tantallon, Nova...
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    Do you have a factory service manual? If not get one, the other books that are out there are useless. Here's the FSM 12 volt diagram-

    [​IMG]
     
  8. Mar 4, 2015
    Greevesman

    Greevesman Member

    Napa, Ca
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    I do have the factory service manual as well as the Moses Ludel book. Neither are as clear as the above. I will try connecting to the armature terminal as you suggest.
     
  9. Mar 4, 2015
    Greevesman

    Greevesman Member

    Napa, Ca
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    You guys rule! I connected the mystery wire to the armature terminal and the Idiot light works fine.
    I am back to the theory that the seller disconnected the wire so I wouldn't realize I had to spend a couple of hundred bucks right away.
    Thanks for the help.
    Greevesman
     
  10. Mar 5, 2015
    1960willyscj5

    1960willyscj5 Well-Known Member

    Mesa, Arizona
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    Is it charging your battery now?
     
  11. Mar 5, 2015
    Greevesman

    Greevesman Member

    Napa, Ca
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    2000 rpm charges at about 13.6 volts. Lite is out. All seems good.
    Wonder what's next?
     
  12. Mar 6, 2015
    Walt Couch

    Walt Couch sidehill Cordele, Ga. 2024 Sponsor 2023 Sponsor 2022 Sponsor

    cordele, Ga.
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    jeep toss
     
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