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Thread: Turn signal wiring issue

  1. #1
    Senior Member Dagwoods's Avatar
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    Turn signal wiring issue

    Good morning,

    Trying to get ready for inspection and I found an issue that I missed involving my passenger front turn signal / headlight wiring.

    Right turn signals works fine until I turn on the headlights (or just turn on parking lights). Then the ps front turn signal stops flashing and just stays illuminated. Also of note, it looks like my ps front headlight is dimmer then the driver side and the parking lamp is brighter than the driver's side. This also affects the hazards. Hazards work fine until I pull the headlight switch in to park (or all the way on).

    I'm using the Ron Francis harness going to weatherpacks. All other lights and blinkers work as expected. Indicator light on gauge also continues to blink with lights on. A quick visual inspection of wire colors at all connections appears to be all correct according to diagram, but I'm obviously missing something

    Any ideas on where to start looking?
    Mk IV base kit #9273 Delivered 1/29/2018
    3-link Moser 8.8 3.55
    TKO 600
    427w by Fordstrokers w/Holly sniper efi/hyperspark distro and ignition

  2. #2
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    Look for a bad ground first.

  3. #3
    Senior Member Dagwoods's Avatar
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    Thanks. That was my first thought as well. All the the other items that the same ground supplies (horn, DS turn signal, and cooling fan) are all working fine. I'm in the process of checking the weatherpacks from harness to turn signal, but my thought is a bad ground would also prevent the turn signal from working without lights on.
    Mk IV base kit #9273 Delivered 1/29/2018
    3-link Moser 8.8 3.55
    TKO 600
    427w by Fordstrokers w/Holly sniper efi/hyperspark distro and ignition

  4. #4
    Senior Member edwardb's Avatar
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    Tell us a little more about your installation. What are you using for the turn signal and hazard switches? LED lights by any chance? Doing anything unusual with the rear lights, like a trailer control module or whatever? Has it ever worked properly?

    As a general comment, in the stock RF harness wired per the schematic turn signals, hazards, running lights, and headlights are all separate circuits. So interactions are not possible in theory. Likely something something wired wrong including possibly backfeeding. Some LED lights have caused these kinds of interactions. Another possibility is the dual filament 1157's in your turn signals/running lights. If clocked wrong (it's possible) or the socket is wired wrong, can cause interactions.
    Build 1: Mk3 Roadster #5125. Sold 11/08/2014. Build 2: Mk4 Roadster #7750. Sold 04/10/2017. Build Thread
    Build 3: Mk4 Roadster 20th Anniversary #8674. Sold 09/07/2020. Build Thread and Video. Build 4: Gen 3 Type 65 Coupe #59. Gen 3 Coyote. Legal 03/04/2020. Build Thread and Video
    Build 5: 35 Hot Rod Truck #138. LS3 and 4L65E auto. Rcvd 01/05/2021. Legal 04/20/2023. Build Thread. Sold 11/9/2023.

  5. #5
    Senior Member Dagwoods's Avatar
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    And the winner is....@edwardb. Standard ffr turn signals. No LED. I thought I had checked them, but apparently only with headlights off.

    I had just got done swapping lights and had concluded the ps light was bad since the DS one when swapped over worked when I saw your reply. Sure enough, took the bad light apart and it was indeed clocked wrong. Pushed it out, turned it and reinstalled. I'm good to go now.

    Thanks. You saved me having to wait for a new light.
    Mk IV base kit #9273 Delivered 1/29/2018
    3-link Moser 8.8 3.55
    TKO 600
    427w by Fordstrokers w/Holly sniper efi/hyperspark distro and ignition

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  7. #6
    Senior Member edwardb's Avatar
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    Cool! Glad it was a quick easy fix. You're not the first to do that. Although I've had people tell me it's not possible. You proved otherwise. Good luck with your inspection.
    Last edited by edwardb; 04-15-2020 at 04:09 PM.
    Build 1: Mk3 Roadster #5125. Sold 11/08/2014. Build 2: Mk4 Roadster #7750. Sold 04/10/2017. Build Thread
    Build 3: Mk4 Roadster 20th Anniversary #8674. Sold 09/07/2020. Build Thread and Video. Build 4: Gen 3 Type 65 Coupe #59. Gen 3 Coyote. Legal 03/04/2020. Build Thread and Video
    Build 5: 35 Hot Rod Truck #138. LS3 and 4L65E auto. Rcvd 01/05/2021. Legal 04/20/2023. Build Thread. Sold 11/9/2023.

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