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Thread: Battery charging circuit question......

  1. #1
    Join Date
    Jun 2004

    Question Battery charging circuit question......

    The alternator does not charge the battery on my 87 DeVille. The alternator is good. The battery charge warning light is out.

    I believe the alternator field energizing current flows through the bulb when the ignition is turned on.

    Can anyone tell me if there is a resistor in parallel with the bulb to allow the current to pass when the bulb is burned out? If so, what is the value and watt rating of the resistor and where is it located?


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  3. #2
    Join Date
    Jun 2004
    Northern Ct.

    Re: Battery charging circuit question......

    The current drawn through the bulb is what excites the field in the alternator, if the bulb is burned out, it won't begin charging. Also,make sure you have power at the stud on the back of the alternator.

  4. #3
    Join Date
    Mar 2004
    Dearborn, Michigan

    Re: Battery charging circuit question......

    I have a similar situation with my 98 Deville

    (Battery & Alternator tested good at the autoparts store)

    My next step is to test the circuit for the regulator.
    My Chilton Manual shows two wires coming off of it.
    One goes to the PCM and the other goes to the Electronic Instrument Panel Cluster.

    My question is this:
    What kind of signals should I be expecting at the regulator harness connector? I am assuming that the instrument panel supplies Positive voltage to the circuit and the PCM supplies the field circuit ground. Am I correct?

  5. #4
    brougham is offline Cadillac Owners Master
    Automobile(s): 1991 Cadillac Brougham D'Elegance 5.7 Litre, 1994 DeVille
    Join Date
    Jun 2003

    Re: Battery charging circuit question......

    The only thing the bulb is there for is to tell you when there's a problem.

    Bring it in somewhere to get the charging system checked. That'll tell you what's wrong.

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