Two Ignition electrical questions discovered during MSD installation

Electrical and Ignition

  1. harrisonm

    harrisonm Well-Known Member

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    Background: 1969 Barracuda, 340, fairly new 650 Eddy Thunder Series carb, orange box Mopar Performance ignition. Car runs fine, but didn't have quite the same punch as last year, so I thought I'd do a few upgrades starting with a complete MSD ignition system (Digital 6AL, Billet Distributor, Wires and Coil). I am very good with regular electric system, but not so much with ignition system. I read the MSD Installation instructions thoroughly and was going to install it today.
    VOLTAGE DATA: The light weight red wire in MSD is supposed to go to the + side of the coil. So I thought I would check the voltage at that spot. With the key in the "ON" position, I only got 5.7 volts. I thought that might be low, so I checked some other voltages and here they are:
    ENGINE OFF: Battery = 12.15V; + coil = 6.2V; inboard side ballast resistor (BR) (single blue wire) 10.3V; outboard side (BR) (brown wire and a blue wire) 6.15V.
    ENGINE IDLE: Battery = 14.4V; + coil = Mostly 9.54V but bouncing between 4.4 and 9.54; inboard side BR = mostly 14.3 but bouncing between 4 and 14.3; outboard side BR = same as coil.
    ENGINE @ 2500 RPM: Battery = 14.6V; + coil = Mostly 11.5V but bouncing between 0.8 and 11.5; inboard side BR = mostly 14.6 but bouncing between 4.0 and 14.6; outboard side BR = same as + coil.
    When I pressed in firmly on the individual BR leads, the voltage bouncing reduced a lot.
    QUESTIONS: 1. Are these voltages expected? I would have expected to see 12 volts at the + side of the coil. The MSD guy said I could use ANY 12 volt switched source for the red wire, but these voltages have me stumped. 2. The MSD guy said to bypass the BR by just taking it out and connecting the wires together. Is that a good idea? What will that do?
     
  2. furyus2

    furyus2 Well-Known Member

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    • RedFish

      RedFish Well-Known Member

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      Most aftermarket ignition sysyems do include a coil that operates on continuous 12 volts so deleting a ballast resistor, tying blue and brown wires together is typical.
      In any case, Before ballast resistor should be close to battery voltage. To delete ballast resistor wouldn't effect this. If you have only 10 volts coming to the engine harness on brown and/or blue wires,,, Ignition switch, bulkhead connections, etc.., can be the point or points of voltage drop. Low voltage might explain why the previous ignition system didn't perform well. Good luck with it.
       
    • harrisonm

      harrisonm Well-Known Member

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      Thanks for your response. The link sends me to the same instructions I have from the box. All the instructions say is to 'bypass' the ballast resistor, and the guy from MSD said all I had to do was take the resistor out and connect the wires together (single blue wire on one side and a brown wire and a blue wire on the other side already together in one plug in terminal. Is that the same as what you are saying? I just don't know what that will do. The guy at MSD said nothing about connecting the start ,and run wire from the ignition switch.
       
    • RedFish

      RedFish Well-Known Member

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      Brown and blue are start and run. Your OEM coil got full voltage at switch start position. The coil got reduced voltage at switch run position through the ballast resistor. You simply tie them together to supply full voltage to the new coil at both switch positions. That's what you do, that's what it does.
       
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      • Garrett Ellison

        Garrett Ellison Amateur driver on public roadway, do not imitate..

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        You have a weak connection at your key switch connector, bulkhead connector, or possibly a wire with an internal break. It's best to correct this before going any further and I would advise to use the key circuit to energize a relay and connect a fusible link wired from the battery terminal of the starter solenoid to the relay contact to energize the MSD unit with the relay. Our 50 year old key switch and terminals oftentimes don't play together too well with modern high demand systems.
         
      • harrisonm

        harrisonm Well-Known Member

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        Thanks for your response. Although I only have 10.3V with engine off at + coil and after side on BR, I do have full voltage of over 14V when engine is running. Is that strange? I am confident that the bouncing voltage readings mentioned above will go away after the BR is eliminated since pushing firmly on the leads got rid of most of it (loos connections?). I may just go ahead and install per MSD recommendations and see what happens.
         
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        • harrisonm

          harrisonm Well-Known Member

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          Thanks again.
           
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          • 69_340_GTS

            69_340_GTS Well-Known Member

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            Ballast resistors suck and are the source of many start/run problems. Do as MSD says and get rid of that thing. I put the exact same "system" on my '69 340 and it made a huge difference, especially with hot starts.
             
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            • harrisonm

              harrisonm Well-Known Member

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              Thanks. Did you follow their instructions exactly? That is, did you just take the ballast resistor out and connect the wires together; and did you connect the original coil + wire to their light weight red wire?
               
            • Mattax

              Mattax Just the facts, ma'am FABO Gold Member

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              Maybe I'm misreading what you did. So go ahead and correct me.
              As far as the MSD goes, you can have crappy connections to the small red wire and it isn't going to matter one bit to the ignition.
              The way I read your first post, you have the red wire attacherd to the coil positive. It shouldn't be.
              Small Red wire connects to the original ignition wire that used to connect to the coil, but does not when using the MSD.
              The MSD Orange wire connects to the coil.

              With the CD box, the energy is built internally using power fed in through the heavy red wire.
              When the spark is signalled, the energy is released and goes down the orange wire into the coil's windings inducing the secondary high voltage to the spark plug.

              VOLTAGE DATA: The light weight red wire in MSD is supposed to go to the + side of the coil. So I thought I would check the voltage at that spot. With the key in the "ON" position, I only got 5.7 volts. Seems about right

              ENGINE OFF: Battery = 12.15V; + coil = 6.2V; inboard side ballast resistor (BR) (single blue wire) 10.3V;
              Why is there only one blue wire at that terminal?
              There should be a blue wire from the key switch crimped onto the terminal next to a blue wire going to the voltage regulator.
              outboard side (BR) (brown wire and a blue wire) 6.15V. That's about right when current is flowing through it.
               
              Last edited: May 13, 2019
            • Mattax

              Mattax Just the facts, ma'am FABO Gold Member

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              Red On-Off Wire: Join this to the original blue coil power wire. Mount it so its insulated from ground and the coil feed. You can use a bolt and spade connection as shown in the photo - these used to come with MSD 6A and 6T boxes. You can leave the ballast resistor and connections for easy return to mopar box or make a new 4 way connection on an insulated stude. Either way the on/off wire will get power whenever the ignition switch is in either run or start. This draws very little power - just enough to turn on an internal switch in the MSD.

              img_7951-jpg.jpg

              Here's the instructions from my 6T. Hooks up the same, just written and illustrated differently.
              autotronics1498p4-jpg.jpg
               
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              • harrisonm

                harrisonm Well-Known Member

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                Thanks. I actually had not hooked up anything yet. After reading the directions, the FIRST thing I did was to test the voltage at the + coil wire, and I was surprised it was so low. I think I will just follow MSD's instructions and the advice from my FABO buddies and put it in tomorrow. Thanks for the picture.
                 
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                • Mattax

                  Mattax Just the facts, ma'am FABO Gold Member

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                  That's the purpose of the ballast resistor. Reduce the voltage of the current flowing to the coil (and also points on a points distributor). Otherwise the coil gets overheated.

                  The question I have was about your other test results. Where is the voltage regulator getting power from?
                  If its not getting power at system voltage, that will cause regulation and charging problems.
                  Originally it came through the wire connecting to the run circuit at the ballast.
                  Should look something like this inside the connector.
                  upload_2019-5-13_18-52-57.png

                  The Brown & Blue pairing is the other side. Blue originally went to coil positive. You can use it for the MSD 'on' switch.
                  Brown supplies power for the ignition only when key is in start position.
                  upload_2019-5-13_18-56-12.png
                   
                • Mattax

                  Mattax Just the facts, ma'am FABO Gold Member

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                  Every place marked V should be the same voltage.
                  If the Alternator out is 14.4 Volts, then all of the other locations should be 14.4 Volts.
                  A voltage drop of a couple tenths is to be expected. More than that indicates a poor connection along the flow path.
                  Of course the illustration is a points system, but the concept is the same with a ECU added.
                  Voltage to the coil should less than V when the key is in run position.
                  upload_2019-5-13_19-22-13.png
                   
                • harrisonm

                  harrisonm Well-Known Member

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                  THANKS GUYS
                   
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