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ignition switch. late 75 wiring, car runs at off position.

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  • ignition switch. late 75 wiring, car runs at off position.

    good morning 6pack.

    the school car has been fortunate in the electrical area, with only a few issues over time, and mostly due to misdiagnosed diagram. it was a few years ago that we realized this 76 car had 75 wiring in it, cause it was built in late 75 as a 76 car. only sharing this lead in for others that may have that light head scratcher.

    driving recently in the rain, my oil light came on my tach gauge. Odd, having great compression, and I know there was a good supply of oil. That went away later, until recently when I turned the car off, and it kept running. switch back to run, still running. switch back to off and it shut down. I don't think its related at the time, but I realize now, it probably is.

    I go out to the car yesterday, ready to take it to lunch on a beautiful north dallas day, turn the key, absolutely dead. I can't remember how old the battery is, pop the hood, 9/17 stamp on the interstate battery. Must be the battery, as i am not remembering those symptoms above. Jumper cables, car fires, voltmeter shows charging, and I think, I must have a draw somewhere - haven't had one before, but must have one now. I know this seems odd to this group, but this car has sat for months, and would still fire with no significant loss in battery.

    I let the car run for about 10 minutes at high idle, shut it off. I work a little, go back out later, bump the starter, and clicks. I think now the battery isn't holding a charge. But I put it on the wall charger for a few hours, now its wine time, so I pull the charger, crank up, head to the store for evening supplies, get to the store, turn off the car, and its still running. Its here that I figure the only way to shut down is to turn the key to the accessory? position. So we are clear. horizontal key, off, 10am, accessory, noon, run. 2pm, start.

    And here is a new wrinkle. With the car in the off position, my electric fan was running. So there is some draw there, even if the fan isn't running, something else maybe is charged in that position. in accessory, car shut down, but the radio was on.

    That may have been a wordy detail into - where should I start looking first? My thoughts right now - its a simple ignition switch, which i think I have replaced once. I know I have pulled this switch in the past, and am comfortable with replacing that. I also have a great wiring diagram - forget who produced those for us, but color coded, and mine is laminated, which I recommend.

    My current work around is - pop the hood, pull the battery cable, lower the hood. as it sets right now. at Run, car is fine. And I could live like this for a while, but my concern is, I think this is progressive, and all that current could be going thru a bad swtich, and cause a fire.

    Thanks for reading. Hope everyone is having a great day. Will add this and a few other items to my new blog today.

    cheers
    G

  • #2
    When the oil pressure light came on in the rain, did the brake warning lamp come on as well?

    When you switch the ignition on before starting the engine, do both the oil pressure and brake warning lamps illuminate?

    You might want to verify that the oil pressure switch is wired correctly. If it's not, it might contribute to the problem.

    Click image for larger version

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    R3
    Jim Herter ͏͏͏͏͏͏͏͏͏͏ Copperas Cove, TX
    Original Owner ֍ 1970 TR6 ֎ CC 50990 LO
    VDU 506H

    Comment


    • #3
      i'll check that today, Jim, thank you. My ignorant question back is, I didnt change anything and its been fine over the years.

      I'm going to pull the switch unit and inspect it. I am not going to dismantle it - i think that is a sealed plastic box.

      Comment


      • #4
        With an ohm meter set on the 200Ω range, check the ignition switch for continuity between terminal 3 (white wire) and terminal 2 (brown wire) in the different switch positions. There should be no continuity in the Off and Accessory positions. You might also check that there is continuity between terminals 2 and 6 (both brown) only in the Off position.

        My comment about the oil pressure switch is kinda far reached. There would need to be some other anomalies in the warning lamp(s) wiring for that to contribute.
        Last edited by RatRidgeRoadster; 10-18-2020, 01:45 PM.
        R3
        Jim Herter ͏͏͏͏͏͏͏͏͏͏ Copperas Cove, TX
        Original Owner ֍ 1970 TR6 ֎ CC 50990 LO
        VDU 506H

        Comment


        • #5
          Thanks Jim - Im pretty sure its that switch, and will follow those instructions - that sounds good, and appropriate. the crossover of current inside that switch, over time, and if replaced like I think it was, the quality may be questionable.

          More to come.

          Comment


          • #6
            update. pics below.

            I haven't tried to start the car, but this may be part of the problem. 2 wires, sheaths gone or frayed. And when I pulled this unit out, those 2 wire areas were touching. I don't know what would have caused the fray, or pushed them against each other. I think I have repaired this before, or maybe even replace it, but looking at the unit and some of these connectors, I don't remember doing any of that.

            so, I am going to seal these 2 wires and replace the switch, and test. Pretty sure this is the issue.

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            • #7
              Overheating of those wires in the past may have turned the insulation brittle. Could the large brown wire on terminal 2 have been in contact with terminal 3 (white wire)? That would explain the run-on problem. No, strike that - it would continue running in the Accessory position.

              The two bare wires contacting each other could explain the dead battery.

              Did you check the low oil pressure switch wiring? That could still contribute to the run-on problem if other conditions are met. If not, I think I'd be looking for a new switch with the pigtail harness.
              R3
              Jim Herter ͏͏͏͏͏͏͏͏͏͏ Copperas Cove, TX
              Original Owner ֍ 1970 TR6 ֎ CC 50990 LO
              VDU 506H

              Comment

              ignition switch. late 75 wiring, car runs at off position.

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