Ammeter Bypass a Must?

Electrical and Ignition

  1. Bodyperson

    Bodyperson Pedal to the metal FABO Gold Member

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    I bought a car with the speculation of flipping it. 65 Impala. The fuse block had more 1/4 inch bolts in it than it had fuses.
    I soda blasted the bulkhead connector along with the fuse block. Rinsed it with electric spray cleaner, installed all of the correct fuses and everything worked as they should. The only draw back was my stupid ass erased all of the information on the fuse block. I printed a picture of the fuse block off of the internet and threw it in the glove box.
     
  2. Ironracer

    Ironracer Gearhead

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    I had to trace mine. Faded, I guess. Or worn out from fuse feelers!
     
  3. RustyRatRod

    RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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    Mine is a 64 Valiant, so it might be different.
     
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    • RustyRatRod

      RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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      Ok, well that splains some of the kornfrooshun. lol
       
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      • Ironracer

        Ironracer Gearhead

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        Just scored one in Canada for 25 bucks + 14 for the ride. Hopefully it's the right one the gauge itself is around but I'm thinking that's my cluster and it's too late to pull it out right now I've got to pull it out tomorrow to put a vinyl overlay on it and I'm fixing to blast the floorboards down, rust encapsulate them
         
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        • jos51700

          jos51700 Green Bearing thread connoisseur

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          The ammeter bypass was never as much about bypassing the ammeter, but more about getting the high current wires out of the bulkhead connector. Running the charging wire directly to battery positive (through a properly sized fusible link, naturally) is really the safest way to handle this, and that takes the ammeter out of the equation anyway, so there is no reason to keep it at that point.
          Disconnect the battery before you do this!
           
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          • 1969383S

            1969383S FABO Gold Member FABO Gold Member

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            For me there was no sense in it. I replaced every harness in the car. I am not pushing any high current and a completely stock electrical. I believe I am good for at least another 40 years!

            This is a good mod when you do anything other than pure stock! Start adding radios and amps or just trying to limp through with older wiring it makes sense! At least to me.
             
            Last edited: Jun 12, 2021
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            • BillGrissom

              BillGrissom Well-Known Member

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              What I'm missing is that if the ammeter failed, the alternator may not be able to charge the battery. If true, you must fix that. The only path for charging current to the battery is thru the "+" terminal on the ammeter and that is a dedicated wire straight to the battery. The only exception is that a few special high loads in the cabin come straight off BAT+ without going thru the dash ammeter - convertible motor, police spotlight, ... .

              As stated, the main purpose of the "MAD Bypass" is to take the high charging current off of the bulkhead connector terminals, to avoid melting the plastic. That happens when the terminals get corroded. Not a problem in 1963 and 1965 cars since they have dedicated buss-bars to feed those high currents thru [ALT (blk) and BAT (red) wires]. But, even with those, if you upgrade the alternator, it might output too much current for the dash ammeter to work safely. My cars all have the 1965 bulkhead (retrofit my 1964). I designed in a large diode pair which allows the ammeter to work normally at small charging currents (due to ~0.5 V forward drop of diodes), but starts bypassing the alternator output straight to the battery thru the diodes at higher currents (I measured ~0.75 V drop across ammeter at full scale). In effect, the diodes act as a "pressure relief valve" at higher currents (either direction, in or out of battery). Search for my post if interested, but don't fool with it unless you are an engineer or skilled tech.
               
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              • RedFish

                RedFish FABO Gold Member FABO Gold Member

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                All OEM equipment did overheat connections in wiring, back when it was all new. Most dangerous scenario was/is jump starting a dead battery. Start the engine with choke set to high idle and the alternator will send all it can through the only path to the battery. You have all new connections going to a 50+ year old amp gauge. That gauge may be your weakest link.
                Adding one wire from alternator to starter relay stud does render the amp gauge inaccurate but it takes the high amp charging load off of it too.
                 
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                • RustyRatRod

                  RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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                  "HOW" inaccurate does it become? In other words, say my alternator quits, will I be able to "see it" on the gauge?
                   
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                  • RedFish

                    RedFish FABO Gold Member FABO Gold Member

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                    Yes you would see discharge. The added wire takes away some of the charging load. One would need to bypass voltage regulator, full field the alternator to see if the amp gauge would still peg on the charge side. That isn't a test I would be willing to do if I did still have the original amp gauge and wiring.
                     
                  • barbee6043

                    barbee6043 barbee 6043 FABO Gold Member

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                    I have had quite a few of these old Mopar over the last 3 decades, some of which I drove to work daily out in the sticks, like 60 mi. I always clean everything about the ammeter and be sure all is tight and good and use it, I like having that working gauge. I myself have never had an issue. Is it very possible I could. I guess so. But my cars are always just stock nothng added to cause a separate issue either.
                    I carry a small fire extinguisher just in case!
                     
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                    • RustyRatRod

                      RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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                      That's an accessory that should be carried in every vehicle.
                       
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                      • 67Dart273

                        67Dart273 FABO Gold Member FABO Gold Member

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                        "From where I sit"

                        1...There are issues with "restoration correct." If you are past all that, then no issue
                        2...All of this depends on the conditions the vehicle experiences, AKA corrosion, humidity, "rust belt" etc, the amount of current, IE accessories, pumps, fans etc
                        3...As mentioned "mostly" the BIG issue is the bulkhead connector. "One way" around that is to snake larger wires directly through the drilled-out bulkhead connector cavities.
                        4....Ammeters vary over the years. One big issue (as my 70RR Ralley dash) was the ammeter in some vehicles is bolted through the PLASTIC housing, so if "anything" gets warm, the plastic softens, the connections get more loose and worsen, and you have a rolling snowball........in this case a fireball

                        Other clusters use a metal cluster and insulating washers. These types clusters are a little better. Another ammeter issue is that the studs are not fastened to the internal shunt. You can "gain a lot" here by soldering or low temp silver soldering the studs to the shunt. Now if you get the nuts tight "as in jambed" you will avoid some ammeter issues
                        5....Likely one of the better ways to go--and most time consuming---would be to convert in some way to an external shunt meter. The C barge cars did this as far back as 71 or 72 I don't remember. This uses a sensitive meter (small wires) which go out into the engine bay and "tap in" to the harness itself and use the voltage drop in the harness to indicate on the meter. One problem with external shunt setups (notably Ford trucks and Rangers) is that they tend to be "numb" that is the needle hardly moves when you turn on the lights at rest

                        6...As others have mentioned IF everything is absolutely up to snuff, IF yo have NO high current accessories and IF you have nothing larger than "say" about a 45A alternator, the OEM system will likely "do ok."
                         
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                        • 1969383S

                          1969383S FABO Gold Member FABO Gold Member

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                          Replace it all! Wiring that is!

                          Always carry an extinguisher!

                          I feel pretty Damn confidant for another 40 years or so! Like said pure 99% stock and likely easier on the electrical with a modern ignition. Enough LED inside to reduce the load without making it modern!

                          Take a minute to read the amps for each lighting circuit you have! You will be Enlighted!
                           
                          Last edited: Jun 21, 2021
                        • 1969383S

                          1969383S FABO Gold Member FABO Gold Member

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                          I reduced my opera lamps in the fish from 2.5 amps each to nearly nothing with LED lamps on both sides!
                           
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                          • RustyRatRod

                            RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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                            If I decide to try adding the wire from the alternator to the starter relay, what gauge would be sufficient?
                             
                          • RedFish

                            RedFish FABO Gold Member FABO Gold Member

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                            I forget what gauge wire and fusible link I used in my 67. I may have written it on the modified wiring diagram that I keep in the car. I'm guessing 10AWG primary wire I had on hand with 12AWG fusible link.
                             
                          • 67Dart273

                            67Dart273 FABO Gold Member FABO Gold Member

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                            Rusty does your car not have the big lugs in the bulkhead for the ammeter? I can never remember what years did / did not. 65 aparrently does I know they skipped a year or two
                             
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