Instrument cluster warning lights on and go off only at 3000 or aboveRPM. 700 1988

Discussion in 'General Motoring' started by Hameed, May 31, 2008.

  1. Hameed

    Hameed Guest

    Only today, my 740 GLE 1988 started like it normally does with no
    problem but the battery and the warning lights didn't go off after it
    started. It kept being on. When I accelerated to up to 60MPH or when
    the RPM went to 3000 RPM the lights fade away and then when the speed/
    RPM go down they lights come back on again.

    I guess it is either the battery- which is sort of strange since the
    car starts with not problem from the first time- or the alternator
    circuitry i.e. it is not charging the battery.

    I think I should take out the battery and get it to Advance Auto parts
    to check the health of the battery and then I can isolate the
    alternator problem(s) later, is that the way to go or what?

    Hameed, May 31, 2008
  2. I would suspect the alternator circuitry. Sounds like you need a new
    brush/regulator set.
    Chuck Fiedler, May 31, 2008
  3. Hameed

    Hameed Guest

    I ran the car and used a voltmeter to see the voltage across the
    battery with car on and off.
    It is around 8-9Volts off and shy of 12Volts when I revv it to 3000
    RPM or so.

    So, I guess the Voltage regulator and the brushes are the easy thing
    to do for now. All connectors seems to be good enough. I have isolated
    the battery terminals and no build up or corrosion is noticeable

    I hope that the alternator is not becoming bad itself. How do I test
    for that?
    fcpgroton has the regulator for $24 and the rebuilt alternator for
    $150. So, I hope I can get away with just the regulator.
    Hameed, Jun 1, 2008
  4. Hameed

    Hameed Guest

    I will take your advice and take the battery to advance auto parts to
    test it. I got this battery from Costco in 2004 so it stayed for
    almost 4 years now so I won't be very sad about it.

    I drove on it like that for around 15-30 minutes.

    I have a question though about the alternator, that I hope someone can
    answer for me, how do I know if the alternator is good or not after
    the regulator and brushes are replaced?
    Hameed, Jun 2, 2008
  5. Hameed

    Perry Noid Guest

    If you're only measuring 8-9V across the battery when the car is NOT
    running, that sounds like you have a bad battery at the very least! Maybe a
    shorted cell in it...

    I think I'd pull the battery, check the voltage across it, and if still low,
    I'd try putting in a new battery and see how things look...

    That's not to say you don't need to replace the regulator or the entire
    alternator, just that you should start with the battery and see. Batteries
    don't last forever, and even a new one can fail....
    Perry Noid, Jun 2, 2008
  6. Hameed

    Ken Phillips Guest


    That's simple, it will either work, generating approximately 13.8 volts
    at fast idle speed with all the electrical equipment that the car has
    switched on, or it won't work, outputting an inadequate low voltage.
    As an aside, I have known a regulator/brush packs to be perfectly OK,
    the alternator to be perfectly OK, but, the output voltage to still be
    low. Causing the car to eventually break down. The problem? Well it was
    simply a dirty contact between the regulator and the alternator (not the
    brushes), once it was cleaned up the alternator worked beautifully.

    Best wishes,
    Ken Phillips
    Ken Phillips, Jun 2, 2008
  7. Hameed

    Hameed Guest

    I have changed the regulator. The brushes were worn out.
    It was not a hard job to do when I changed the regulator and brushes.

    The battery was fully charged when I tested it in Advance Auto Parts
    and they left it for 20-30 minutes until it was fully charged.

    Now, the battery reads 12.5 volts without connection.
    It measures after the car is started and the lights are on 11.99Volts.

    I guess I am not seeing the 13.5volts because the battery is already
    charged, right?
    Hameed, Jun 7, 2008
  8. Hameed

    Ken Phillips Guest


    Apologies for sounding pedantic, but, I'm not clear what you mean when
    you say "after the car is started". Is the engine actually still running
    while you are measuring the battery voltage? Is the ignition warning
    light extinguished when the engine is running?
    If so, then even with a depleted, but, otherwise good battery, the
    terminal voltage of the battery should still be in the 13.5-13.8 volt
    range (sometimes a little bit higher), even if everything electrical is
    turned on. Sometimes the engine needs to briefly run at about 1000 rpm
    to properly energise the alternator.
    If the above isn't seen, then check the earth wire to the alternator
    body from the engine block, the B+ wire (thick red one) to the battery
    via the starter solenoid, and if possible the integrity of the ignition
    lamp wire, following it (the thin wire) from the alternator to the grey
    multi pin plug at the side of car.
    Look for breaks, inappropriate grounds/shorts, worn/missing insulation,
    and frayed connection terminals.

    Ken Phillips, Jun 8, 2008
  9. Hameed

    Hameed Guest

    No problems at all.

    I drove the car after I changed the regulator and I measured across
    the battery and it is 14 Volts.
    With no the car off, the volt was 12.

    So, I guess everything is in order now.
    Hameed, Jun 11, 2008
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