Key on and cranking power wire?

Discussion in 'Magnum Engine Swaps' started by dragbaron, Mar 25, 2018.

  1. dragbaron

    dragbaron Well-Known Member

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    Doing my second A-body magnum EFI swap on a friend's '72 Duster. When I did the swap in my Scamp a couple years ago, I couldn't find a wire that had power with the key in the run and the crank position, so I had to toggle switch the power wire for the computer. Thought maybe it was a problem with the car.

    Now on this Duster I'm having the same issue. What are you guys using to power the computer?
     
  2. 1994redram

    1994redram FABO Gold Member FABO Gold Member

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    I use the coil wire to trigger my fuel pump relay. I tap into it right before the ballast resistor
     
  3. roccodart440

    roccodart440 Well-Known Member

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    There is one over there. Maybe a red one? I had this issue with my MSD. Chased the problem for days. Finally accidentally started while jumping the solenoid manually under the hood while testing for spark.
     
  4. dragbaron

    dragbaron Well-Known Member

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    No luck, it's just like the first magnum EFI swap I did. I even back probed the wires at the ignition switch harness connector can't find a wire that has power when on and when cranking. The only cranking power wire I found was the one for the starter relay. Any other key on power wire I find will lose power when I go to crank.
     
  5. 1969383S

    1969383S FABO Gold Member FABO Gold Member

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    There is not one off the ignition switch. You have a wire usually yellow for crank to the starter relay but not one in both run and start.

    Edit:

    Is not one wire to the ballast hot for both? Brown on 70 and early models.
     
    Last edited: Mar 28, 2018
  6. RedFish

    RedFish Well-Known Member

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    You should have a brown and a blue at the ballast resistor. One is hot in start, the other hot in run. Most simply twist these 2 wires together for aftermarket ignition with e-coil. Those don't require a ballast resistor/reduced coil voltage in run.
     
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    • dragbaron

      dragbaron Well-Known Member

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      Ballast resistor and voltage regulator are long gone. I found the two blue wire connector for the resistor and it has power in the run position. I found a brown wire with no connector on it and it only shows power when I hold the key right in between run and crank.

      I remember when I did this swap on my Scamp a couple years ago, that I back probed every single wire coming out of the 3 bulkhead connectors and the only wire that had power at the crank position was the wire for the starter relay. The Scamp was a running car when I did the swap. Now this Duster is exactly the same way. It seems like something happens when all the original wiring is not connected to anything.
       
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      • RedFish

        RedFish Well-Known Member

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        I've seen ignition switches loose connections. Coil would emit 1 spark as key turned back to run.
        So... go under the dash to the switch harness connector. See whats hot and whats not in the different positions.
        PLEASE NOTE; You cannot tap the yellow wire to substitute brown. The backfeed from blue to yellow would keep the starter engaged in run.
         
      • dragbaron

        dragbaron Well-Known Member

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        Yeah, definitely can't use the starter relay wire for that exact reason.

        I already back probed the ignition switch connector, and it's the same thing. Brown wire has power right in between run and crank and the yellow wire is the only wire that has power in the crank position.

        I need to check my Scamp and see if the brown wire is doing the same thing, as I never held the key between run and crank on it. This Duster hasn't had a motor in it for years, but the Scamp was a running car before the swap, so obviously it had power to the ignition when the key was in the crank position.

        I have a '71 D100 I plan on doing another magnum swap to. Maybe I'll put a battery and it and see if I can find a cranking power wire on it. It has no motor in it, so the wiring isn't connected to anything either.
         
      • aaadave

        aaadave Well-Known Member

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        when i did my magnum swap, i just connected the brown and blue wires together and run them to the pdc. been working fine for 3 years.
         
      • mopar65

        mopar65 Well-Known Member

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        The blue or blue/white strip wire is your 12V with key on and the brown wire is your 12V start wire.
         
      • dragbaron

        dragbaron Well-Known Member

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        That's what I originally thought, but to have two cars in a row where the brown wire doesn't have power in the crank position made me think that maybe I was missing something.

        I still need to go out to the '71 D100, that is the next magnum swap, and see if I can find a crank position power wire.
         
      • mopar65

        mopar65 Well-Known Member

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        The 71 Duster I did and my 73 dart the brown wire was 12V crank.
         
      • 67Dart273

        67Dart273 Well-Known Member

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        ALL older Mopar ignition switches work the same, unless they are defective

        1...You have power in...............

        2...You have ACCESSORY power out to the ACC fuse buss and is hot only in run and ACC

        3...You have the (usually dark blue) "run" (IGN1) which is hot ONLY in run, not start.......

        4...You have the (usually brown) bypass (IGN2) which is hot ONLY in start, not run. This is the one goes to the coil +

        5...You have the (usually yellow) "start" wire hot only in start and what feeds the starter relay

        The yellow and brown are drawn wrong in the 73 book, maybe others. The 73 diagrams suggest that yellow and brown are connected. THEY ARE NOT. They come off separate distinct switch poles in the ign switch, otherwise they would backfeed.
         
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        • 67Dart273

          67Dart273 Well-Known Member

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          If you are NOT using a Mopar factory ignition switch, there are a few ways around the problem............

          If you need a "hot" source in "start."

          DO NOT just hook to the "start" wire as this will cause a backfeed situation in "run."

          You can........hook a sizeable diode in series off the start terminal and use that for your source, just parallel it with "run."

          You can........use the later model "Jeep" starter relay which has one more terminal and use that terminal

          You can......use some other relay and just parallel the coil of the second relay right across your starter relay, so it "comes alive" with the starter relay, then power the contacts from a battery source, and the other contact goes to "run."
           
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          • dragbaron

            dragbaron Well-Known Member

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            I bought a new ignition switch, so when it comes in I will just plug it in under the dash and see if that gives me cranking power at the brown wire. If that doesn't work, it'll probably have a toggle switch like my Scamp.
             
          • RedFish

            RedFish Well-Known Member

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            The aftermarket replacement switch may not be simple plug and play. Some have a extra small gauge black wire that isn't used in majority of applications. If you find this black wire is connecting to any other color wire in the cars harness connector, STOP. Clip this black wire and dead end it. All wires req'd should match color to color.
             
          • dragbaron

            dragbaron Well-Known Member

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            It does have a black wire that lines up with an orange wire at the plug, so I should cut the black wire then I guess.

            On a positive note, it works! I now have power at the brown wire in the crank position! Woohoo!
             
          • 67Dart273

            67Dart273 Well-Known Member

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            So old switch was bad?
             
          • RedFish

            RedFish Well-Known Member

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            What I do is relocate the orange wire. Make it up outside or beside the OEM connector with male and female spade terminals. This allows their black wire to dead end where it is. If/when it needs the same switch again... no questions.
             
          • dragbaron

            dragbaron Well-Known Member

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            Yeah, that was the problem. I wonder if that's the same problem with my Scamp now.
             
          • dragbaron

            dragbaron Well-Known Member

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            Is the orange wire just for lighting up the gear selector? I always thought any orange wires in the interior harness were for lighting.
             
          • RedFish

            RedFish Well-Known Member

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            enough chit chat
             
            Last edited: Apr 15, 2018