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Amps gauge resistor?

Discussion in 'Gauge, Speedo & Instrumentation' started by MikecLA, Jul 30, 2020 at 1:29 PM.

  1. MikecLA

    MikecLA Junior Member

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    Going through my gauges, my temp gauge has a resistor that you can clearly see the orange between the two posts. But my amp gauge has what looks like a blank ceramic resistor?
    Is it supposed to have a 90 on resistor here?
    - I’m replacing the two inline 4amp fuses as well. Thanks

    781C0CE8-299A-46D3-BC77-A62D817AF95A.jpeg
     
  2. MikecLA

    MikecLA Junior Member

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    crickets....
     
  3. Goldie Driver

    Goldie Driver Full Access Member

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    I will try to remember to look at the spare cluster this weekend that I have. Ammeters stopped after 75 IIRC so only someone with a '73 - '75 will be able to answer, and that is if they have looked for this.

    @eskimomann209 - do you happen to have any back side pics of the gauge cluster I got off you ?

    Thanks !

    Britt
     
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  4. Turbo4whl

    Turbo4whl Full Access Member

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    Trying to remember, doesn't the amp meter run the full alternator load, so you see the rate of charge, or discharge?

    Blank ceramic just an insulator?
     
  5. MikecLA

    MikecLA Junior Member

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    That would make sense, blank. Just reading the difference on both sides. Thanks for looking.
     
  6. Snoots

    Snoots Supporting Member Supporting Member

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    For safety's sake, if you are going to continue to run a Ammeter; install ALL new wire for it. That old wire is going to heat up and cause trouble.
     
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  7. eskimomann209

    eskimomann209 Supporting Member Supporting Member

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    I do not. Is there something in specific you need to see?
     
  8. Goldie Driver

    Goldie Driver Full Access Member

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    Just trying to help out the OP if you happened to still have pics.

    Thanks, though !

    :waytogo:
     
  9. Turbo4whl

    Turbo4whl Full Access Member

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    Roger has a good point. The original 10si put out 37 amps. Higher like 55 or 61 amps for options like AC. There must be a good reason GM and others dropped the amp meter in favor of a volt meter. These are all higher amperage than the generators that were used years before.
     
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  10. 75gmck25

    75gmck25 Full Access Member

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    The amp gauge in the squarebody does not flow the full amperage, so it is not going to cause a fire if you install a high amperage alternator. The amp gauge uses the wiring of the truck as a shunt and “calculates” the amperage to display on the gauge.

    - One side of the gauge connects to wiring very near the alternator output wire. Let’s say that shows 13.9 volts.
    - The other side of the gauge connects to the wiring very near the dash. Let’s say that shows 13.75 volts.
    The gauge is designed to use that .15 volt drop in voltage to display an assumed amperage flow on the gauge. It was probably calibrated when new but by now the resistance of the wiring (which is the electrical shunt) is now much different than new . This is why these gauges are so far off as they get older.

    Using a shunt is common for older automotive diagnostic gauges to measure amperage. Its based on the fact that E(volts) = I (amps) times R (ohms).
    If you have a known resistance value (the shunt), and voltage measured at each end of the shunt, you can calculate the amperage.

    Bruce
     
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  11. idahovette

    idahovette Full Access Member

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    Could you put a newer voltage gauge in place of the ammeter gauge and what would have to be changed?
     
  12. Snoots

    Snoots Supporting Member Supporting Member

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    Yes.
    Get a stock GM Voltmeter.
    Remove the Ammeter from the dash.
    Put electrical tape over the printed circuit that fed the Ammeter.
    Attach a wire to one side of the Volt Meter to ground and another wire to the Ignition side of your power (Hot when the key is on).
    You're good to go.

    Drink beer.

    Note: DO NOT remove the resistor from the Volt Meter.
     
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  13. idahovette

    idahovette Full Access Member

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    OK thanks @Snoots, I knew someone could help! Right now it's too hot out to do any work on the square, but I' gonna take your instructions to drink beer to heart.....er belly!!!! Thanks Roger
     
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