Turn signals occasionally do/don't work

Discussion in 'Troubleshooting & Diagnosis' started by MP81, Aug 21, 2019.

  1. MP81

    MP81 Veteran Member

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    Yet another "project" my car has given me...but I noticed this earlier in the year as well.

    This one is pretty simple to explain: sometimes my turn signals will work and sometimes they don't. As far as I can tell (and from just checking), they do not illuminate on the cluster, nor do they work on the exterior - however, the hazards do work.

    I just had the steering column apart (this started happening before I took that apart) and the turn signal switch seemed fine, at least from just looking at it:

    https://scontent.fdet1-2.fna.fbcdn....=4c3e898ea28387c6dd91360c21c6f93b&oe=5DD70633

    Is it the switch/cam in the column (would be a bummer to have to disassemble what I just put back together - and that harness seems like a PITA to run down and out the column), or could it be something else?
     
  2. Twisted_Metal

    Twisted_Metal Administrator Staff Member Lifetime Gold Member

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    That could be caused by a bad connection at the signal flasher (it is separate from the hazard flasher) or several places in the wiring harness.
    It could even be a dirty contact at the switch in the column.
    Thankfully, You don't have to tear the whole column apart to check the contacts at the switch or the harness contacts where they exit the column.

    A short inside the column is unlikely as that would tend to blow fuses but a broken wire in there could make it a real pain to troubleshoot and fix.
    For your sanity... I hope that's not the problem!

    It both sides don't work at the same time, I would be looking at the flasher contacts or the flasher itself.
    You can switch the flashers around to see if the problem follows a flasher but simply unplugging them and reseating them could possibly "fix" the problem if there's any corrosion on those connections.

    Good Luck!
     
  3. MP81

    MP81 Veteran Member

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    Yeah, neither side will work when it's decided not to work. They'll both work when it decides to work again.

    I'm assuming I should be able to use a test light at the connection down under the dash to see if the switch is sending any kind of signal?
     
  4. Twisted_Metal

    Twisted_Metal Administrator Staff Member Lifetime Gold Member

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    And the dash indicators work the same way?

    If so, that narrows down the problem quite a bit.

    What year... 81?

    I’ll try to remember to get back to this thread after I check the wiring diagrams in my old Haynes manual.

    I’m thinking it’s going to be in the power side of the circuit (or the flasher), rather than a problem in the front or rear harness.
     
  5. MP81

    MP81 Veteran Member

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    Yup - when the dash indicators work, the exterior signals work and the relay clicks, and when they're not working, nothing lights up and no clicking.

    Yeah, '81, correct.
     
  6. Gary S

    Gary S Administrator Lifetime Gold Member

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    Start with the easy things. First switch the flasher units and see if the problem moves to the hazards. After that, you can start on the complicated things.
     
  7. Twisted_Metal

    Twisted_Metal Administrator Staff Member Lifetime Gold Member

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    Power seems to come from the fuse block feed and through the flasher, first.

    I'm trying to eliminate parts of the circuits involved....

    The background lights in the dash and the signal indicators share the same ground.
    If the background lighting works when the signals don't... I doubt the problem's in the cluster harness/ground.

    At the signal switch... the circuit splits off into multiple paths, for right/left, front/rear.
    When it reaches the column connector, the circuit branches again, back to the dash indicators.
    I think we can now safely eliminate all of the cluster and connections there.

    The front right/left share a ground and the rear right/left signal lamps do too.
    Those connections are probably buried in a harness wrap somewhere and probably NOT the issue if both sides and front/rear all fail at the same time. I also doubt it's BOTH power sides of the harness feeding the lights is at fault because the hazards use the same circuits on the front ands rear of the car.

    You can use a 12V lighted probe type tester to check the under-dash circuits. If it lights up bright, you know you found power. (It's a cheap simple to use tool and you don't need to measure the actual voltage.)

    From the flasher in the fuse block... There's a purple (14 ga) wire supplying power to the circuit at the signal switch.
    (It should be visible where the under-dash harness connects to the column harness)
    Check for power at the purple wire, with the key on.

    The brown 14 gauge wire next to it should have power with the key on or off... It's for hazards.

    If you don't have power to the steering column circuit (purple - 14 ga)... It's probably the flasher or it's connection at the fuse block. (80 & 81 have two flashers plugged into the fuse block. Other years only have one.)

    Unplug the flashers and look for corrosion and test for power in the fuse block connections. (One side should have power.)

    If you have power to the purple wire at the steering column connection but no power at any of the lt blue, dk blue, yellow or green wires WITH the hazard but NOT with the signals on (key on)... The problem is probably the switch itself or a broken purple wire inside the column. (Meaning... Replace switch and it's harness. :( )

    I don't know if the switch can be disassembled, inspected and cleaned or repaired without pulling the harness though the column but I hope the problem is BEFORE the column.

    I not a professional in this field of work but I've got manual with the diagrams. :)
     
  8. Twisted_Metal

    Twisted_Metal Administrator Staff Member Lifetime Gold Member

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    upload_2019-8-21_19-23-13.png

    I circled my suspected problem areas. ;)
     
  9. MP81

    MP81 Veteran Member

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    Wow, that was incredibly thorough, thank you! I do have a test light - invaluable tool for sure!

    I think that's going to take a second read to comprehend a bit more, haha - so, if the hazards work but the turn signals don't, my mind leaning towards thinking it's somewhere between the switch and the "main" power wire to the turn signals might be correct? Neither front nor rear signal, nor the corresponding cluster light works with the turn signal (I had the the key set to ignition on, so they should have, if they were behaving), but all six work with the hazard light.

    Or does the hazard have its own power feed to the turn signals (that's probably the 9PM lack of comprehension in my brain talking there)?
     
  10. Twisted_Metal

    Twisted_Metal Administrator Staff Member Lifetime Gold Member

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    If I'm reading the diagram correctly... Yes.
    The hazards have a separate circuit supplying power to the column.
    (#27, Brown wire at the harness/column connection)
     

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