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F134 Starter Switch

Discussion in 'Early CJ5 and CJ6 Tech' started by Don X, Sep 12, 2021.

  1. Sep 12, 2021
    Don X

    Don X The Prodigal Moderator Staff Member 2021 Sponsor 2020 Sponsor

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    My M38A1 has a starting problem. It has not been started since I rewired it. I used a wiring harness specific to M38A1s.

    According to the schematics (see pics) everything is correct. A multimeter shows 24 volts at the battery and starter. When the key is turned to the on position all of the gages work so juice is flowing between the starter to the ignition switch. I also have 24 volts at the distributor.

    The starter switch is on top of the starter and is activated with a foot plunger. When depressed I get absolutely nothing. I've confirmed the foot plunger is aligned properly and the rod is being pushed into the switch correctly.

    All of this has me thinking it's the starter switch unless I'm missing something. Before spending $120+ on a new switch which will take 10 days to arrive, is there a way to bench test the switch? I've had it apart and, while the contacts aren't perfect, they look clean enough to work.

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  2. Sep 12, 2021
    Twin2

    Twin2 not him 2022 Sponsor 2021 Sponsor 2020 Sponsor

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    I would try a set of jump cables between the two starter posts
    as to starter switch . can disc be flipped and studs rotated 180°
     
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  3. Sep 12, 2021
    Glenn

    Glenn Kinda grumpy old man Staff Member

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    Correctly as in you're positive it pushes in far enough?
     
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  4. Sep 12, 2021
    Don X

    Don X The Prodigal Moderator Staff Member 2021 Sponsor 2020 Sponsor

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    Yes
     
  5. Sep 12, 2021
    Glenn

    Glenn Kinda grumpy old man Staff Member

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    The only other thing is like Ron said try jumper cables across the switch. You are obviously aware that the key doesn't have to be on for the starter to turn over, right?
     
  6. Sep 12, 2021
    Glenn

    Glenn Kinda grumpy old man Staff Member

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    Can you try a test light across the terminals? Do you have a matching voltage test light?
     
  7. Sep 12, 2021
    Don X

    Don X The Prodigal Moderator Staff Member 2021 Sponsor 2020 Sponsor

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    Great suggestion. I'll try it when I'm back out there next weekend.

    Yes.
     
  8. Sep 12, 2021
    jeepdaddy2000

    jeepdaddy2000 Member

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    Or you could use an ohm meter and test for continuity with the plunger engaged. If you get infinite resistance, you can try testing the plunger by hand. If it is fully engaged and no continuity, you should be able to disassemble it and inspect the contacts.
     
  9. Sep 12, 2021
    PeteL

    PeteL If it wasn't for physics, and law enforcement... 2022 Sponsor 2021 Sponsor 2020 Sponsor

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    M38A1 don't got no key. :confused:



    Try jumping it as said (in neutral!) and also confirm that the adjustment really is forcing full contact.

    Then, I would take it apart and clean it up, or and/or reverse the contacts, etcetera.
     
  10. Sep 12, 2021
    Glenn

    Glenn Kinda grumpy old man Staff Member

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    His does. A picture confirmed it. :) We both know a key switch isn't stock.
     
  11. Sep 13, 2021
    Keys5a

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    Glenn nailed the issue in post#5. If adjusted correctly, the starter should engage and turn the engine over without any consideration of the ignition switch. The foot pedal mechanically mashes the starter contacts together, energizing it.
    The ignition switch (no key originally) simply provides juice to the gauge cluster and the distributor/coil.
    You should also have a 3 lever multi-position switch for lighting.
    My bet is the mechanical plunger on the starter isn't fully hitting home. You should be able to test this by depressing the foot pedal with a multmeter between the two large terminals. I see the copper buss from the terminal to the starter. This assumes the starter motor itself is a known good unit. Check the connection of that buss on the starter?
    -Donny
     
    Last edited: Sep 13, 2021
  12. Sep 13, 2021
    amboynut

    amboynut Member

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    If you are testing resistance across the terminals with the plunger depressed (should be zero ohms) DISCONNECT THE BATTERY FIRST!
    In fact be certain there is no voltage whenever you measure resistance in any circuit. Your meter will not tolerate any voltage when measuring resistance.
     
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  13. Sep 13, 2021
    Don X

    Don X The Prodigal Moderator Staff Member 2021 Sponsor 2020 Sponsor

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    The ignition switch is not in question. It's the starter switch. I suppose I could generically refer to it as a solenoid but it's actually a switch that is activated by the plunger. Everything is line ups correctly and the plunger fully extends when depressed. I've also manually pulled the lever that the plunger pushes without anything other than I can hear the contacts inside the switch hitting each other.

    Next weekend I plan to jump the 2 terminals as previously suggested. If the starter cranks I'll know it's definitely the switch. I opened the switch up to examine it and it looks fairly simple. The contacts don't look out of the ordinary but I don't know what ordinary really is.

    All of the replacement switches that I've been able to find appear to be NOS so I doubt the contacts by themselves are available.
     
  14. Sep 13, 2021
    Glenn

    Glenn Kinda grumpy old man Staff Member

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    I assume that it worked previously but the wiring needed help is the reason you rewired it? If so it would seem you would at least get some indication of the switch working.
     
  15. Sep 13, 2021
    Howard Eisenhauer

    Howard Eisenhauer Super Moderator Staff Member

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    There's one lug on a cable that's going to the switch that looks like it got toasty hot, I'd pull it off & go at it with some sandpaper on the flats just to make sure you get good continuity through to the switch post.
     
  16. Sep 13, 2021
    PeteL

    PeteL If it wasn't for physics, and law enforcement... 2022 Sponsor 2021 Sponsor 2020 Sponsor

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    And, that would likely happen from a dirty contact within the switch.
     
  17. Sep 13, 2021
    Howard Eisenhauer

    Howard Eisenhauer Super Moderator Staff Member

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    Could be but the stud looks fine. :shrug:
     
  18. Sep 13, 2021
    PeteL

    PeteL If it wasn't for physics, and law enforcement... 2022 Sponsor 2021 Sponsor 2020 Sponsor

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    It's a mystery.
     
  19. Sep 13, 2021
    Glenn

    Glenn Kinda grumpy old man Staff Member

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    I think that is just the way it is. I've seen some others somewhere like that....just don't remember where.
     
  20. Sep 13, 2021
    Don X

    Don X The Prodigal Moderator Staff Member 2021 Sponsor 2020 Sponsor

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    The lug is much cleaner than it looks. It was cleaned up on a wire wheel. The multimeter shows 24 volts at the stud so it's conducting well.
     
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