Amp gauge not working now

Discussion in 'Electrical and Ignition' started by Steven190, Oct 7, 2018.

  1. Steven190

    Steven190 Well-Known Member

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    My amp gauge now is not working after I did a parallel 8 gauge wire from the alternator to the started relay stud. I would have thought that it would still work since it is getting voltage through it.
    I guess my question is why it did not work? I will probably just disconnect it and splice the wires together. I drove the car and noticed it was not working, so I got concerned that the battery was not charging. After my drive I checked the battery and it had 12.5 volt in it, so it was being charged.
     
  2. grjammer

    grjammer FABO Gold Member FABO Gold Member

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    Sounds like it is shorted out. If everything else was working except the amp gauge and it worked before, I would bypass immediately to avoid a melt down. The 12.5 Vdc at your battery does not guarantee it is charging, you are just reading battery voltage. It should read higher at the battery while running then not.
     
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    • kursplat

      kursplat FABO Gold Member FABO Gold Member

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      off hand? you made a better, (shorter with larger wire), connection. electricity is lazy
       
    • grjammer

      grjammer FABO Gold Member FABO Gold Member

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      current follows the path of least resistance. as kursplat said, you effectively bypassed your ammeter, it will not work in parallel with a solid wire. if you want it to work, add new larger wiring around the bulkhead connector to the gauge, then back out. there are numerous posts on here concerning the "MAD" ammeter bypass modification. A search should turn up any info you need.
       
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      • toolmanmike

        toolmanmike FABO Staff Staff Member FABO Gold Member

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        Remember, amp gauges need to have all the current pass through it (in series) not just some of it. When you did the bypass the current goes through it and not through the gauge.
         
      • jos51700

        jos51700 Well-Known Member

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        It's an amp gauge, not a voltmeter. Bypass it in the engine compartment, hurt your shoulder patting yourself on the back, and think about the fact that your chances of having noxious smoke come pouring out from under the dash while you're driving just went WAY down.
         
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        • Mopar Tim

          Mopar Tim FABO Gold Member FABO Gold Member

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          My '69 has a Amp bypass, but the gauge is still hooked up, funny thing, when it is charging, the gauge shows discharging...the current is flowing thru the gauge in reverse..I have learned to live with it. All the wiring is solid, so it is staying that way.
           
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          • 67Dart273

            67Dart273 Well-Known Member

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            You made what amounts to a parallel path. You can probably just leave it alone

            If you learn how shunts work, that is how tiny meters measure large current. You take a sensitive meter, would would be "exploded" by a few microamps or milliamps, and put it in parallel with a large conductor. The conductor carries a majority of the load and it is carefully calibrated to allow "just the right" amount of current through the meter to operate.

            If your ammeter was less amps full scale, say, 1 or 10 instead of 30-40A, and the shunt was smaller, say no 12 instead of "whatever," the ammeter would still show some activity

            In fact, in the early 70's, when Ma FINALLY improved the ammeter situation with the "big boats" they did just THAT. Used a charge wire with no "full current" ammeter. Then used a small scale, sensitive meter, and hooked the meter leads up to the big wire "in the harness" so that the harness wire ITSELF made the meter shunt

            GM, Ford, Chrysler, all did this same deal
             
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            • toolmanmike

              toolmanmike FABO Staff Staff Member FABO Gold Member

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              Just thinking out loud here. This would be too simple if a inductive pick up coil could be used. I have a inductive amp pick up on the pid controller I built. A/C though.
               
            • Steven190

              Steven190 Well-Known Member

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              What prompted this was I am using a PowerMaster 75 amp alternator. They told me to use a 8 gauge wire for the power supply. I looked at the MAD threads and made the parallel connection.
              I am going to bypass the amp gauge, I do not want a fire or burnt wires. I looked at the wires now and they are good. It does not bother me that the gauge does not work, it was concerning that it did not move while running. I am going to remove the wire from the back of the gauge. it is a real pain in the engine compartment.
               
            • phaelax

              phaelax Well-Known Member

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              This! Happened to me on the highway. Ended up melting half the wires under the dash