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55 - flickering GEN light

Discussion in '1955 - 1966 Classic Ford Thunderbird' started by TommyDanger, Aug 8, 2019.

  1. I have a flickering gen light. The gen light is lit bright when key is turned on but car not running, which I believe is correct. Then when the car is running, the gen light is dimmer but seems to flicker. Is this from low charging from the generator? Car has 6v fully charged battery. I tested for any drains on the battery (found a couple and disconnected them).
  2. In 1955, the electrical system of the Thunderbird was 6 volt positive ground. If your Thunderbird is a 1955, with a 6 volt, positive ground system, the battery resting voltage is 6.3 volts and the charging voltage should be about 7.1 volts. The exact charging voltage may be as low as 6.6 volts or as high as 7.3 volts.

    Take a multi-meter and set it to measure DC voltage, then measure the voltage across the positive and negative battery terminals with the engine off. On a 6 volt system, a fully charged battery should read a resting voltage of 6.3 volts. After you start the car you should see a charging voltage of about a volt higher than resting voltage. If the reading doesn’t increase by about a volt or if it stays at the resting voltage, it means that the alternator isn’t recharging the battery. This could be because the battery is defective, alternator is defective, the regulator is defective, or the wiring between them has failed.

    With the engine running, if the generator light stays on at full brilliance, you have no voltage at the voltage regulator terminal that goes to the armature. The armature is acting like a dead short and that causes the bulb to glow. This is why the generator light is on before the engine is running.

    If the generator light glows dimly or flickers, the voltage at the armature is low. Sometimes this is caused by low engine RPM. If the light goes out when you accelerate it could be normal or your voltage regulator might need adjustment.

    Another cause of a generator light glowing dimly or flickering could be a poor ground somewhere. This will often reverse the current through the dash light in search of more ground. Another cause is the generator. The brush springs are not strong enough or the brushes are sticking in the holders.

    A basic charging system health test: Use a multi-meter to measure the resting and charging voltages as described above. Then, with the engine running, gradually increase the electrical load by turning on the headlights and the blower fan. Then increase the engine RPM to about 2,500 as you watch the reading on the multi-meter. If the voltage stays about a volt higher than resting voltage, then the car’s charging system is functioning. But if the voltage drops or increases dramatically at any point, there’s a problem with the alternator or the voltage regulator.

    1955 Thunderbird Blue
  3. Thanks for the help!

    I did the test with a multimeter on the battery voltage when the car is running.
    Not running = 6.5
    Running = 6.3

    Seems as though the charging system is not working properly. I had recently resolved a couple battery drains so I'm confident I don't have a drain or short, unless I missed something. Is there a way to test the regulator? How in depth is changing the springs and/or brushes on the regulator?
  4. From your voltage readings, it appears that the generator isn’t charging at all. When I rebuilt my 6 volt generator, I used an article that Bill Abate submitted to the Early Bird magazine as a guide. Attached is Bill’s article along with some pictures showing you how worn my brushes were before I replaced them.

    1955 Thunderbird Blue

    Attached Files:

  5. Thanks for the info and photos. I will pull the regulator tomorrow and see how the brushes look.
  6. So I tested the generator and it seems as though the generator is putting out 7.5 volts. at the voltage regulator. Here are my voltmeter readings:

    Ground - ARM - 7.5v
    Ground - Field - 4.6v
    Ground - BAT - 6.3v
    Battery Terms - 6.5v not running - 6.3v running

    I also did a generator test by jumping the field to armature posts on the generator and metered the generator with the car on at 14v. I follow a video by Moss Motors on how to test a generator.

    If I am reading the results correctly, the charging problem may be with the regulator. Any insights? Is the regulator adjustable?
  7. Yes, the voltage regulator is adjustable. Attached is the second article that Bill Abate submitted to the Early Bird magazine which covers the voltage regulator.

    1955 Thunderbird Blue

    Attached Files:

  8. Ended up installing a new voltage regulator. All charging seems to work now. I have 7.2 volts at the battery when running!
    ak7an likes this.
  9. Change the voltage regulator, it will solve the problem I am sure, I have just added some light in my trailer which we use for 24/7 towing service nyc.

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