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  1. #1
    FEP Senior Member liv2roc's Avatar
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    Default Charging Problems.

    My 84 mustang gt350 is all stock with a small cam in it. having problems with my battery charging. for years now with the lights on at idle they go dim and brighten up when I rev it up. if I check voltage at idle it is battery voltage if I rev it up to 2000 it goes up to 13.5. its got so its not wanting to start, it will click a few times then start. I dont want to convert to 3g or nothing. but what could be problem, alternator, voltage regulator? what should I change first?

  2. #2
    FEP Power Member
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    Default

    If it goes up to 13.5 Vdc then the regulator is doing its job. You can rebuild you alternator to have a higher output and looks the same.
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  3. #3
    FEP Super Member gr79's Avatar
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    Default checks and inexpensive simple diagnostic tools

    I use one of these tools all the time to check electrical anything:
    https://www.harborfreight.com/7-func...ter-98025.html
    Use it to check new batteries on shelf when the time comes. 12.6v is good to go fresh.
    Check current car battery water level and voltage first, engine off, all power drains off.
    Attachment 126050

    Check alternator output, ground cables, wiring in harness, connections, belt+tension, parasitic power drain engine off.
    Usually external regulators are fine, especially Motorcraft. Check it's harness plug, tight mounting of regulator to metal.

    This tool works good for quick checks home and on the road, engine running or not. I stow one in console just in case.
    https://www.harborfreight.com/12v-al...ter-63592.html


    Retrofitted a 70a large case 1G alternator long time ago. Exide Classic 96RC battery.
    Picked a new battery off the shelf that read 12.6v. Many did not.
    Have fog lights, large stereo amp, rear defog grid, seat heater. No dimming of anything, recharges battery quickly.
    VDO volt dash gauge is installed. Monitors charging volts and drain. Valuable. At idle, reads 13.5v+ everything on.
    Does taper off some after driving for a while.
    Last edited by gr79; 01-25-2019 at 03:13 PM.

  4. #4
    FEP Senior Member liv2roc's Avatar
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    Default

    its was the alternator. checked it 2 days ago and was getting 13.5 when I reved it up, today it was 11.6 idle and reving

  5. #5

    Default

    14.2 to 14.8 is a pretty normal charge voltage at RPM. 13.5 was a little on the low side.

    Kenny

  6. #6

    Default

    Anything below 12.6 is actually discharging the battery. I would want 13.5 or higher at idle with a peak around 14.2v.

    The battery isn't even charging at idle.
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  7. #7
    FEP Super Member gr79's Avatar
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    Default

    Yes my volt gauge reads just above 14v at max charge rate, even at idle.
    It drops when every possible item is on, rainy night, stereo full blast, waiting at traffic light.
    Once car is warmed up or moving when cold, returns to 13.5-14v+.
    640w stereo amps suck up power.
    Last edited by gr79; 01-25-2019 at 08:21 PM.

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