turn signal issue

Discussion in 'Electrical & Audio' started by 87silveradok20, Mar 20, 2017.

  1. 87silveradok20

    87silveradok20 Full Access Member

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    I have a 1990 chevy crew cab. when i put either turn signal on, all the lights in the front flash together (side markers and the ones below the headlights). Both turn signal lights in the dash blink as well. The rear lights however function properly as if nothing was wrong. I have cleaned up both grounds on the core support. all 4 lights blink full strength. any ideas on what could be the problem? truck has a western hauler conversion on it if that changed anything.
     
  2. chengny

    chengny Full Access Member

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    Did this just start happening out of the blue, or were some repairs/modifications done prior to when it began?

    Have you recently changed a bulb in any of the front sockets?

    Does it matter if the parking lights are on or off?
     
    Last edited: Mar 21, 2017
  3. 87silveradok20

    87silveradok20 Full Access Member

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    well the truck has been sitting for a while and im pretty sure it was happening before that so i dont really remember when it started. i took out all the bulbs and still had the problem and the parking lights beong off or on doesnt matter
     
  4. 87silveradok20

    87silveradok20 Full Access Member

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    Does anyone have any ideas as to what this could be?????? The weather is getting nicer and I would like to drive this truck!!!
     
  5. chengny

    chengny Full Access Member

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    Levi, I hate to say it but, there's not going to be any silver bullet for this problem. You have a crossfeed issue with the two front turn signal circuits (14 LT BLU and 15 DK BLU).

    I don't get this:

    i took out all the bulbs and still had the problem

    How is it possible to have the problem (all the front directional lights come on when either side s selected) if the lamps were all out?

    Anyway, if you have thoroughly checked the three ground points (2 sheet metal points and one on the frame):

    [​IMG] [​IMG] [​IMG]



    If you have gone through all the sockets and checked for shorts - and proper grounding - in each one. And made absolutely sure that the correct bulbs are installed in each socket. The park/turn lamps are 1157 and the markers are 168. The turn signal/marker light circuits are involved and very ground dependent:

    [​IMG] [​IMG] [​IMG]

    Note how the lamp grounds (incl the headlights) are all spliced together - one bad socket or one wrong lamp in a socket and the whole front lighting system is connected to some extent.


    [​IMG]

    If you have checked all that, and you still can't find any path for one circuit to feed over to the other, you will have to start cutting wires. Here is where the two front turn signal circuits enter the engine compartment. If you make cuts in strategically placed spots in the circuits, it will help you narrow down the location of the problem.

    And try this first:

    Remove all the front lamps - at the same time. When they are all out, set your meter to continuity and connect one probe to the 14 circuit and the other to the 15 (use the park/TS sockets). If you probe at the sockets, Be aware that all of these sockets have a lead on the 9 (parking lights) circuit - as well as one from either the 14 (LH) or 15 (RH) directional circuit. So be sure you put your probe on the correct contact at the bottom of the socket.The markers will only have 2 - a 9 and a 14/15. The park/TS sockets will have 3 leads, but only 2 contacts at the bottom of the socket (9 & 14/15) the other lead (ground - BLK 150/151) goes to the socket wall.

    If, with all the lamps removed, you get continuity between the 14 & 15 circuits, the short will be either in the run from the firewall connection block to the front lights - or it could be in the wiring up to the dash indicators, or the directional switch or the wiring that runs up through the column to the directional switch.

    Cut the 14 & 15 right at the FW connector:

    [​IMG]

    If you lose continuity, the short is in the cab - in one of the places noted above.

    [​IMG]
     
  6. Georgeb

    Georgeb Full Access Member

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    @Old77 this needs a sticky!
     
  7. Old77

    Old77 Super Moderator Staff Member

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    Done!
     
  8. 87silveradok20

    87silveradok20 Full Access Member

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    I checked all grounds and when i took all bulbs out, both arrows still blinked in the cab. The lights on the back of the truck however still blinked normal. I guess im gonna have to pull the connector on the firewall and see how many terminals are getting power. I would have the tendency to belive it was a short if all 4 lights werent on full strength.
     
  9. Georgeb

    Georgeb Full Access Member

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    At this point I would disconnect the turn signal switch and check to see if you get continuity on the two wires mentioned When you are supposed to. This will determine if the signal switch is good or bad. Then move down the line to the next connector.
     
  10. 87silveradok20

    87silveradok20 Full Access Member

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    is there a separate switch for front and back or ust one?
     
  11. Georgeb

    Georgeb Full Access Member

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    The rear lights use different contacts in the turn signal switch so technically yes.
     
  12. chengny

    chengny Full Access Member

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    Yeah, but the thing is - you're not looking for a short to ground - you have a short from one turn signal circuit to the other.

    This is different than a direct short to ground - where there is good metal to metal contact between a hot conductor and the body/frame. Since there is no resistance in the circuit, the amount of current that is able to flow is unlimited - and as a result, the fuse blows immediately.

    It's also different than a ground fault - where there isn't direct (metal to metal) contact of a hot lead to the chassis but there is still some current flow to ground. The resistance - caused by paint, rust, grease, etc - is what limits the current flow and as a result, the associated fuse doesn't fail. In that case the lamps in a lighting circuit would tend to go dim/blink slowly, or if it's a circuit supplying a motor - the motor will run slow.

    But the increase in total load/voltage drop due to the condition you are experiencing is minimal. Therefore you probably won't see a change in flash rate or any loss of brightness in the associated lamps.

    The marker filaments are so fine and draw such a tiny amount of amperage, that the addition of an extra one has essentially no effect on total circuit load (same goes for running the additional indicator lamp in the instrument cluster).

    So, what it really comes down to is you are powering just one additional filament - the directional filament in the park/TS bulb for the unselected side. That's not nearly enough added current to cause either dimming, a slow flash rate or a blown fuse.
     
    Last edited: Mar 26, 2017
  13. 87silveradok20

    87silveradok20 Full Access Member

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    Would this cause the side marker lights to not alternate with the front ones?
     
  14. Georgeb

    Georgeb Full Access Member

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    They will only aternate when the running or headlights are on. Otherwise they flash at the same time as the fronts.
     
  15. 87silveradok20

    87silveradok20 Full Access Member

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    ok wow i did not know that. i will try turning the lights on and see if that changes things
     

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