69 L 46 proper voltage readings at the coil for start and run - NCRS Discussion Boards

69 L 46 proper voltage readings at the coil for start and run

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  • Michael L.
    Extremely Frequent Poster
    • December 15, 2006
    • 1390

    69 L 46 proper voltage readings at the coil for start and run

    Guys,

    Still working on fixing the car. Waiting on a my carb to be sorted out and double checking everything in the meantime. At one point I thought someone had posted that the reading on the coil for start and run were 12V in the start position and 9V in the run position. My car seems to be the opposite, with 9V in the run position and 12V in the start position. Which is correct?

    Mike
  • Richard G.
    Extremely Frequent Poster
    • July 31, 1984
    • 1715

    #2
    Re: 69 L 46 proper voltage readings at the coil for start and run

    12V (battery voltage during cranking) is supplied to the coil while cranking.
    With the key in the run position the voltage drops because the ballast resister (or resistance wire) is in the circuit.

    Test the wires with them both disconnected from the coil. That way you should get reading you can relay on.
    Rick

    Comment

    • Hank D.
      Very Frequent User
      • January 1, 1999
      • 137

      #3
      Re: 69 L 46 proper voltage readings at the coil for start and run

      You want the lower voltage in the run position. That's the job of the ballast resistor - it reduces the voltage in the run position so you don't burnout your points prematurely. You should have full voltage in the cranking / start position.

      Comment

      • Michael L.
        Extremely Frequent Poster
        • December 15, 2006
        • 1390

        #4
        Re: 69 L 46 proper voltage readings at the coil for start and run

        OK so my car seems correct then. I can't test the wires separately as the harness has them crimped together. See the attached pics.

        Mike

        coil wire A.jpgcoil wires.jpg

        Comment

        • Michael L.
          Extremely Frequent Poster
          • December 15, 2006
          • 1390

          #5
          Re: 69 L 46 proper voltage readings at the coil for start and run

          OK so now when I check the voltage in the run position I get only 4 volts and in the crank position I still get 12V. What could cause the voltage to drop so much in the run position?

          Mike

          Comment

          • Michael L.
            Extremely Frequent Poster
            • December 15, 2006
            • 1390

            #6
            Re: 69 L 46 proper voltage readings at the coil for start and run

            While I've been trying to sort out the car in the last few days I've had to charge the battery and I've cranked the car with the charger in place. Not sure how that could affect things but I'm consistently now only getting 3.8V to the coil in the run position. Earlier on in this saga I did have 9V with the key in the run position. Is it possible to burn out the resistance wire with what I've been doing and get the resulting voltage drop? I've inspected the ends of the wire and it seems fine.

            Comment

            • Duke W.
              Beyond Control Poster
              • January 1, 1993
              • 15663

              #7
              Re: 69 L 46 proper voltage readings at the coil for start and run

              It's not clear to me how you are measuring voltage. Cranking voltage is measured during actual cranking, and voltage at the coil should equal battery voltage due to the R terminal on the starter solenoid bypassing the resistor. Cranking voltage should be no less than about 10.5V if the battery is of proper capacity and in good condition.

              Running voltage should be measured at idle speed, and should be a bit more than half of system voltage, which should be in the range of 13.5-14.5V if the alternator is functioning properly, so voltage at the coil should be about 7-9. You can also measure it with the engine off/ignition switch on as long as the points are CLOSED.

              Duke

              Comment

              • Michael L.
                Extremely Frequent Poster
                • December 15, 2006
                • 1390

                #8

                Comment

                • Michael L.
                  Extremely Frequent Poster
                  • December 15, 2006
                  • 1390

                  #9
                  Re: 69 L 46 proper voltage readings at the coil for start and run

                  OK so I realized the only thing I changed when the noted the voltage drop was swapping out the OEM coil for an MSD master blaster 2 coil. Using this coil with the points closed I get the 3.8V I mentioned earlier. With the OEM coil swapped back in I'm getting the 7V you mentioned at the coil. When the car was running briefly earlier I measured the 9V.

                  I noticed that when I pull the coil wire off and crank it I get a decent spark from it, and when I pop the cap and crank it the points are getting a pretty robust spark, but I'm getting only a weak/intermittent spark when I pull a plug wire. I'm using the date coded packard suppression wires I got from one of the vendors. Any chance it could be the wires? I don't see how they could go bad just by sitting but maybe I'm wrong. These are the wires I used for the dyno run so at that time at least they seemed to work fine. Maybe I should swap them out?

                  Mike

                  Comment

                  • Duke W.
                    Beyond Control Poster
                    • January 1, 1993
                    • 15663

                    #10
                    Re: 69 L 46 proper voltage readings at the coil for start and run

                    ...don't know anything about the aftermarket coil. OE type RFI wires should measure no more than 5K ohms per foot. The repros have a spotty reputation. Also a high voltage aftermarket coil could break down the insulation. They were only designed to handle up to about 25KV. If a plug wire opens up and the coil generates 40K open circuit voltage it could break down the insulation.

                    The OE single point ignition system is pretty good - simple, reliable - other than the sloppily assembled distributors, which are easy to fix. I always recommend keeping them OE equivalent with new or good used parts since a lot of repro stuff seems to be iffy, but guys don't listen and end up with a kludge of aftermarket parts.

                    Duke

                    Comment

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