1. gm1236

    gm1236 Well-Known Member

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    I ran the voltage test, I found about 1.5 volt drop at the bulk head connector. After that connection the rest of the system didn’t drop much. I have about the same voltage on the inside of the bulkhead connector and at the battery when the car is running.
    I ran the test with an old alternator and everything seem to settle down, the amp gauge was about 1/2 way between the middle and full charge. Then I put the original alternator back in and things went haywire again. Amp gauge was way up and the alternator belt was squealing a little, like it was really working. Output voltage went up to around 17. So I was starting to put the other alt. Back in and the connector pulled off the positive field wire and i stopped there. I’m going to solder on some new terminals.
    Could this alternator that’s acting up be a 65 amp? I did notice in my wiring diagrams it shows different wiring for the 65 amp alt. This car also has a single pole ballast resistor, shouldn’t it have a dual being a ‘75?
     
  2. Mattax

    Mattax Just the facts, ma'am FABO Gold Member

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    The voltage drop is proportional to the resistance AND the current flowing through that resistance.
    Is this 1.5 Volt drop in the alternator output wire connection?
    So putting these together, if the ammeter is showing 1/2 way up the charge level, that's about 20 amps to the battery.
    The alternator field and the ignition are taking abother 5 amps. So that's about 25 amps through the alternator output wire.

    Its not clear to me whether the newer one is acting up, or is cabable of providing much power at idle speeds than the old one.
    All alternators produce much more power above idle speed. Lets say when regulated to 14 v the old one maxes out at 25 amps at 650 rpm, and the new one can produce as much has 45 amps at 650 rpm. And lets say the battery is low and when given power at 14 V will try to draw 50 amps. That creates lots of problems most of which are obvious - such as 40 amps is more than the circuits are made to handle - charging a battery that fast will cause it to get hot and charge poorly - maxing out the alternator is hard on its wiring. Another is that the voltage drop at the connector will be nearly twice what it was with 25 amps flowing through it. Voltage drop = current x resistance.

    I would start by cleaning the terminals. Tighten them up as needed and make sure they are secure when you reinstall. Look at the wire condition at the crimps as well.
    You can find some posts about disconnecting the bulkhead connector, as well as removing the male and female terminals.
    New seals are available from DMT.

    If the terminals are compromised there are a few different ways to improve the flow path.
    Some people drill straight through the connectors and join the wires. I don't like that because it makes it difficult to service and diagnose any of the other circuits in that connector.
    My suggestion is to take a cue from one of the methods mopar used when installing high output alternators. The most common one people have posted photos of here seems to be on cars equiped with rear window defroster grids.

    What I did on my '67 was a parallel wire feed to terminal stud. This is similar to what Chrysler did for some 60 and 65 amp alternator equiped cars with options other than the rear window defrost.

    upload_2020-10-14_23-5-53.png
    I chose to use the terminal mounted in the factory location because I wanted to power the MSD, and didn't want it pulling power through the ammeter.
    In this car the alternator output terminal in the bulkhead was OK, but had some overheating damage. Damage I can almost certainly pin on a low battery recharging situation.
    So the way its wired now there are two paths from the alternator to the main splice. Current will take the path of least resistance, normally the shortest but this way there is some redundency.
    upload_2020-10-14_23-20-7.png

    If you have no need for a terminal stud, you can run the parallel wire direct through a grommet to the ammeter's stud. This assumes your ammeter is relatively accessible and that it is an internally shunted ammeter.

    Anyway the point is there's a number of ways to skin the cat besides drilling through the existing connector.
     
  3. Mattax

    Mattax Just the facts, ma'am FABO Gold Member

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    I beleive you are correct. However the second resistor, which was 5 ohms, was to regulate power to the ECU. Later ECUs, and most (possibly all?) replacments today handle this internally.
    But it does suggest someone has done some rewiring.
    Some of the 60 and 65 amp alternators had different voltage regulation wiring than standard Chrysler alternators.
    All cars equiped from the factory with 60 or 65 amp alternators had a heavier output wire and a grommet through the firewall as part of the arrangement.
     
  4. Mattax

    Mattax Just the facts, ma'am FABO Gold Member

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    To illustrate the current relation to voltage drop.
    upload_2020-10-14_23-51-41.png

    V=I x R
    1.5 Volts = 25 amps x Resistance
    .06 Ohms = Resistance.

    Lets now say the current is 45 amps.
    The votlage drop will increase proportionally.
    V = 45 amps x .06 Ohms
    V = 2.7 Volts
    Now what's the regulator going to see and how will it react?

    Once the battery is charged (or replaced if defective), the typical current flow will be 5 amps or less.
    Now what happens to the voltage drop?
    V = 5 amps x .06 ohms
    V = .3 Volts
    Everything works like normal...
    until the lights and other stuff is turned on...
     
  5. gm1236

    gm1236 Well-Known Member

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    Thanks Mattax,
    The bulkhead connection on my car looks like it has been hot, I planned on bypassing it, but your suggestion of a second wire may be an easier option. In the photo, the red wire powers the MSD, the black wire from the harness is from the alt. Stud, where does the other black wire going through the firewall connect?
    Thanks again for the reply, very informative.
     
  6. Mattax

    Mattax Just the facts, ma'am FABO Gold Member

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    It goes to the ammeter's black terminal. I had the instrument panel out anyway for speedometer repair so this was a good time to do it. The ammeter connections in the rally panel are difficult to access with the panel installed so I had been waiting for the opportunity.
    upload_2020-10-15_22-59-48.png
    I used a small grommet in the firewall but was considering a factory style one if I could have found one. They look like a big bottle stopper. If I had also run the battery wire through the firewall I would have kept looking for a bigger grommet.

    Your '75 firewall may be a little different, but the indentations for various unused optional pass throughs will be there.
    Here I'm starting to mockup the length of the wire from the alternator.
    upload_2020-10-15_22-46-5.png

    upload_2020-10-15_22-49-11.png
     
  7. gm1236

    gm1236 Well-Known Member

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    Thanks Mattax, I’m going to pull the gauge panel and see how it looks. Is the black amp gauge wire where I want to connect the wire from the alt? I’m thinking of running a second wire, rather than bypassing the connector.
     
  8. Mattax

    Mattax Just the facts, ma'am FABO Gold Member

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    Yes. Chrysler seemed consistant with that. Red for battery connection and black for alternator output.
    The back of the ammeter may even have R next to the stud for the red wire. At least on mine, there was no mark on the side connecting to the alternator/main splice.

    In '67 the wires were 12 ga. '75 might be 10 ga ?? Cars with the rear window defroster grids got 8 ga!
    I'd suggest 12 AWG Marine wire at a minimum, and 10 ga would be better. Marine wire is made with smaller strands and is slightly denser for the same gage diameter tha automotive gages. I find its also easier to work with. Due to the restrictions on in-person retail I ended up ordering 10 ga GXLautomotive from Wirebarn for the main run to the stud.

    The ammeter studs were #10 and the alternator output stud 1/4" diameter. Look for ring terminals with decent contact surface but not so big as to risk easy shorting.
    I saw a lot for sale on-line that had insulation that looked like it would get in the way of the connection. :(
    The ring terminals I bought were 'F-crimp' - IIRC made by AMP - TE Connectivity
    upload_2020-10-17_7-29-30.png
    They were actually a bit of a pain to work with. I had to trim the wings a little to fit the wire tightly and due to the thickness they didn't crimp easily.
    upload_2020-10-17_7-33-29.png

    Then heat shrink tubing to cover the crimp area.
    ---

    For something to compare the condition of yours to. This was the condition of the bulkhead terminal from the alternator when I checked on it in. The rubber seal had melted and there is slight discoloration of the metals but overall not terrible. This is part of a 25 yr old replacement harness. I'm pretty sure the damage was done 2016 when I was forced to recharge a very low battery off the alternator.
    upload_2020-7-1_17-37-20-png.png
     
    Last edited: Oct 17, 2020
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    • gm1236

      gm1236 Well-Known Member

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      I ran a 10 ga. Wire from the alternator to the post with the black wire on the ammeter. The ring terminal on the red wire had been replaced and looked corroded, so I replaced that also. I solder and heat shrink all the connections.
      I ran the new wire, put everything back together and drove the car. The amp gauge stayed between the middle line and full charge line and seem to be charging more the longer I ran it. So I took the battery out and charged it, it was very low, took a few hours to get back to normal. I did put another know good battery in and the amp gauge stayed between the center and + middle charge line, but I was getting 15 volts at the battery. The voltage drop from the alternator to battery is less than 1 volt now. I’m going to put the charged battery back in and see what it does.
       
    • gm1236

      gm1236 Well-Known Member

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      With the 2nd alternator and s fully charged battery everything seems ok. The ammeter is running just right of center. I have less than 1 volt drop from alt. To battery.
      Thanks again Maddax and 67dart273.
       
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      • Mattax

        Mattax Just the facts, ma'am FABO Gold Member

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        Seems like you got it, or at least the worst of it.
        If you still find difference between the alt out and the VR, column connector is another place to look.
        That carries a fairly high load when the choke assist is on, and when accessories are on (wipers, turn signals, etc).
         
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