Losing switched power and other #$%&^# electrical issues. HELP!
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Thread: Losing switched power and other #$%&^# electrical issues. HELP!

  1. #1
    Newb Mopar to ya's Avatar
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    Losing switched power and other #$%&^# electrical issues. HELP!

    I need some help. My 73 Dart Sport, 408 stroker / 200 4R, has been running great for 6 years. A month or so I came home from a car show and it would not shut off. Key turned off, key in hand, but it stayed running. I didn't notice it before, but I drove it a week later and noticed it wasn't charging as well. It seemed like it was the ignition switch, so I installed a brand new one. Same issue. I had 12.6v at the battery and only 10.8 at the alternator. I started tracing the power to the alternator and after a little checking I found the car wouldn't start. The MSD ignition wasn't supplying power to the coil. I had constant power and ground, but I found the switched power to the MSD had 12v key on, but lost all power during cranking. If I added 12V to the switched line the car starts. I draw the switched power from the ballast resistor, and have since I put the motor in. I have key on power at all four terminals but lose power to all four when cranking. It seems to me that my new ignition switch is bad, but I am looking for opinions, ideas, etc. When I ran power to the MSD box and got it running today it still wouldn't turn off with the key and was not charging. I have to believe they are all related and that in the end one repair will fix all the issues. HELP!

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  3. #2
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    Sorry to be so late to reply but just now noticed the thread. This sounds like two independent problems that I cannot find a way to relate to each other. Not turning off is either a faulty ignition switch or a melted wiring harness. The ignition switch has an ignition run position where power is applied to the blue wire that connects to the ballast resister, voltage regulater/alternator and choke thermostat heater (in stock form), and a start position where power is applied to the yellow start relay wire AND to the brown ballast resister bypass wire that provides full 12V to the coil during cranking so as to give the hottest spark possible during start up. If 12V is missing during cranking you have lost continuity between the ignition switch brown wire and your MSD box. If the engine won't turn off then the blue 12V run wire is somewhere melted into the red B+ supply wire or the alternators black charge wire. The whole thing sounds like a wiring harness melt down somewhere most likely under the hood where all the heat is. Since the brown wire in question terminates at the ballast resister location and goes no where else I suspect you can limit your search to the area between the ballast resister location and the ignition switch. I have seen rub through damage near the master cylinder on a firewall wiring harness hold down strap that caused an under hood fire (black alternator wire rubbed through to the metal tab) so I suppose other scenarios are possible in that location such as the brown or blue wire melting into the black or red wires which would cause both symptoms simultaneously. I hope you can figure it out.

  4. #3
    Newb Mopar to ya's Avatar
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    It ended up being a melted wiring harness. The B+ wire to the alternator was melted and fused with the field wires and five other wires. It as quite a mess.

  5. #4
    Full Member kendog170's Avatar
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    Good that you found it. Better than sweeping up the ashes !
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    500 Stroker finally done . Now restoring my 340 4 Speed Ragtop .Hidden Content

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