Ignition switch wires identification

Electrical and Ignition

  1. SalC

    SalC Well-Known Member

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    I've rewired my 75 Duster using EZ's Wiring harness. All is good but I'm having trouble getting the ignition switch wired properly. I replaced it with a new switch, only difference is there is one extra black wire which is smaller - I'm just not using it. My problem is I can start the engine but when the key goes back to "run" position it kills the engine, I lose +12v at the coil (in my case +12v to the MSD box I have).

    My question, there are 5 wires and here's how I have them identified based on the wiring diagrams. What does each do? Based on the diagram I should be using the brown wire to the coil but my continuity test proves I have continuity from the red to brown in crank position but it opens in "run" position (which makes sense why it kills the engine in run mode)

    Red - Main Power
    Black - ? (have connected but not sure what this is)
    Brown - Coil +
    Blue - Alt & Voltage Reg
    Yellow - Starter relay (start)

    I have the brown wire feeding the + coil or in my case the 12v switched input to the MSD box.

    Here's a few pics and my continuity test:

    20170310_150806 (Medium).jpg

    20170310_142842 (Medium).jpg

    Switch.jpg

    EZ.jpg
     
  2. DDodger

    DDodger Well-Known Member

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    You need to find a manual and look up your factory ignition switch colors. I don't remember what small black is, might even be ground

    You have a terminal went to the ballast in start

    You have the run terminal. Both need to be jumpered together

    On older cars this is brown (start) and dark blue (run). Check your switch against a diagram for the right colors.
     
  3. DDodger

    DDodger Well-Known Member

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    Looking at what you posted below, I'd say jumper blue and brown

    Black would be your accessories, like heater and wiper
    Red - Main Power
    Black - ? (have connected but not sure what this is)
    Brown - Coil +
    Blue - Alt & Voltage Reg
    Yellow - Starter relay (start)
     
  4. SalC

    SalC Well-Known Member

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    DDodger looking at it again I think you are correct. What's missing in my setup is the ballast resistor. The brown bypasses the resistor during "start", and once the ignition switch drops back to "run" the blue takes over. Since I'm not using a resistor if the brown and blue were tied together I'd get +12v during start and run. Brilliant! Thanks!

    Brown and Dark Blue.jpg
     
  5. SalC

    SalC Well-Known Member

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    Works fine with brown and blue jumpered. Problem solved.

    Thanks for your help!
     
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    • ScampMike

      ScampMike Despicable Damn Yankee

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      too cool!! :thumbsup: - nice job - both of ya!!!
       
    • 77D100

      77D100 New Member

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      Don't know if i'll get a reply as i seem a little late to the party. I have a 77 D100, a904 trans with an msd 6al box. Last summer my ignition switch got sloppy and wouldn't start the truck anymore. So i replaced the switch, still doesn't start. The msd box is wired a little different than msd says to, ie_ small red wire from box is wired to a keyed 12v wire as my original pos coil wire (pink) is wired to the elec choke on carb because it originally had man choke and the ground wire for the box is grounded on the frame. Worked fine this way for 11 years. I haven't changed anything only cleaned up the wires and got rid of the wire nuts and old butt connectors. Currently running a momentary button to start it, wire from pos battery to switch then other side of switch to relay. My original signal wire is grounded to the battery as for whatever reason had a small amount of voltage through it while motor was running and when grounded went to zero on the volt meter. I don't know what changed but it's driving me nuts trying to figure it out. Thanks everyone 20220410_150313.jpg 20220410_150006.jpg 20220409_171030.jpg
       
    • 67Dart273

      67Dart273 FABO Gold Member FABO Gold Member

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      You should have started your own thread, but "anyway." The "usual suspects are thus:

      Most Mopars have TWO wires involved with ignition "run" and "start." IGN1 "run" goes from the key, through the bulkhead, into the engine bay, and supplies several loads, depending on year. Ignition power to the ballast resistor, alternator field, VR, choke if used, and smog doo dads

      THAT POWER, the "run" power, NORMALLY GOES DEAD during cranking!!!!

      IGN2 is the ballast resistor bypass circuit. It goes from a dedicated contact on the ignition switch, through the bulkhead, to the coil+ side of the ballast, and is ONLY hot during cranking. It supplies hot battery starting power direct to the coil and "backwards" through the ballast to the ignition box during cranking

      "It may be" that your old ignition switch did not do that, and that IGN1 (your choke wire) got power during start, and that the new switch does NOT

      ALSO IN THE MIX is that at some point, Ma went to what "I" call the "jeep" style starter relay which had one more contact and one more terminal. I believe it may have some interaction with that circuit in later years. Not sure when they made that change (top left terminal in diagram)

      You may need to "find" your ballast bypass/ IGN2 wire and connect it to the small red on your MSD, along with the original "run" power wire

      JEEP starter relay diagram-001.jpg
       
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