2001 blazer battery light flashing

Discussion in 'Chevy S10 Forum (GMC Sonoma)' started by Jimbo88, Mar 19, 2017.

  1. Jimbo88

    Jimbo88 New Member

    Hi guys, new here. I've searched everywhere for answers to my problem with no luck. Found this forum so hopefully someone can help. I have a 2001 blazer lt 4wd 4.3l vortec. The alternator went bad few days ago. I drove it about 8 miles, from work to home then parts store. I bought new alternator. Installed it right there. Truck starts, alternator charge at around 14.4 or so volts. And the battery light flashes with no pattern. On a few seconds off a second, on 15 seconds off, etc,etc. had the alternator tested and the battery. Both are good. All fuses are good, and no loose wires. Battery doesn't discharge while driving. Sitting in truck for about 15 mins, turned on lights, radio. Without engine running. Started engine and voltmeter sits just below 14 volts until I rev engine a little. Meanwhile battery light still flashes. Anyone have any ideas what the problem is?
     
  2. RayVoy

    RayVoy Rockstar 4 Years 5000 Posts

    So, no real pattern to the flashing?

    I've never had it, but I'm guessing a poor connection, maybe a wire broken inside the insulation. I'd be suspect of the red wire from the alternator to the battery.
     
  3. Jimbo88

    Jimbo88 New Member

    No broken wires, have 14.4 volts at back of alternator and it's also at the battery
     
  4. RayVoy

    RayVoy Rockstar 4 Years 5000 Posts

    Ok, can you monitor the voltage and watch the light flick at the same time?

    When the light turns on does the meter change at all, just a very small change may be all you see unless you have an old meter with a needle.

    So, here is the theory. The computer monitors the output of the alternator, when the voltage drops below a threshold the light will come on.
    Somewhere between the alternator output post and the input of the computer, you must have a poor joint, or a broken wire.
     
  5. Jimbo88

    Jimbo88 New Member

    I'm checking the voltage right now, I ohmed the wires from the plug in the alternator back to the ecm and they are good. As far as a voltage drop according to the dash gauge no, but I'm checking with my meter now. I'll reply with results in a few minutes
     
  6. Jimbo88

    Jimbo88 New Member

    I have a digital meter, it goes from 14.69 to 14.68 but not with the light flashing. Voltage at the plug on the alternator is 2.5 on the grey and 1.09 on the red
     
  7. Jimbo88

    Jimbo88 New Member

    When I turn on rear defroster, and heater blower I get 5.2-5.6 volts on grey wire and red wire stays at 1.1. And using anolog meter now but no fluctuation on charging voltage with light flashing
     
  8. Jimbo88

    Jimbo88 New Member

    Well after the 3rd alternator, it's fixed. The light was flashing because the amps were low on the alternator. It was charging at 14.4 volts. So the light runs of the amps, and the gauge shows the volts
     
    silverado002 and RayVoy like this.
  9. silverado002

    silverado002 Rockstar 3 Years 1000 Posts

    Good for you. That 14.4 volts is a good voltage but like you found out the amperage is just as important or more so. Remember the old days when there was an ammeter gauge instead of a voltmeter. It really told the story on alternator to battery charge.
     
    Jimbo88 likes this.

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