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Thread: Turn Signals Donít Work When Headlights On

  1. #1
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    Turn Signals Donít Work When Headlights On

    So just yesterday I posted a great video of how I had all my lights working with the RT system and an LED conversion. Turn to today, I get home, want to hear the car rumble after a long day and while it’s running decided to test the lights again...turn signals don’t work. Shut things off, try them again with the engine off works fine. Engine off, headlights on, turn signals don’t work. I have went through every scenario I can think of to narrow it down and come back to somehow the headlights/parking lights are feeding back to the turn signals some how and knocking out the flashers. The electronic flashers do not click when the headlights are on and turn signals are switched on as well. They do click when the headlights are off and left, right, and flashers work as the should. I don’t understand how this is happening when the headlights and turn signals are on different circuits.

    I have the RT turn signal system, LED package from Watson’s Streetworks, and electronic flashers

    Need some help with this one.
    Last edited by Cruzzz; 10-01-2019 at 11:07 PM.
    MKIV #9542 Complete Kit, Coyote, IRS - Delivered - 2/19/19, First start - 9/8/19, Go Cart - 9/14/19
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  2. #2
    Boydster's Avatar
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    First thing I'm going to say is start checking all your grounds. Remove lamps one at a time to see if it starts working normal, then go after the ground on the one that changed it.

    Bad / odd grounds can do all sorts of weird stuff. When something doesnt make sense, especially in a simple DC system... go for the grounds.

    I once had a turn signal that was backfeeding into the ignition switch, and every time it flashed, it turned the entire car on & off. You guessed it... bad ground.
    ---Boyd---
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    Senior Member edwardb's Avatar
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    Agree checking grounds is the first place to look. Went back and watched your video again. Don't see the specific combination you're describing in the video, e.g. turn signals plus headlights at the same time. Did this work before and now doesn't? That would be a pretty big clue IMO. If it never worked, could be ground but also could be something miswired. Agree as well the turn signals and headlights are on completely difference circuits and if all is right shouldn't interact. Bad ground(s) or some kind of backfeeding (via miswire) can do all kinds of strange things though.

    BTW, off topic but in your video don't see the gauge backlighting coming on. Needles yes, but no backlighting. Dimmer turned down? Or not working?
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    Quote Originally Posted by Boydster View Post
    "... I once had a turn signal that was backfeeding into the ignition switch, and every time it flashed, it turned the entire car on & off. You guessed it... bad ground."

    Sorry for your trouble, but this is a pretty cool (even if maddening) scenario! This would be the first time I have ever heard of a good excuse NOT to use your turn signals!

    Cruzzz- Boyd and Paul have given you solid advice! Good luck running it down.

    Regards,

    Steve

  7. #5

    Steve >> aka: GoDadGo
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    Steve's Stupid Questions Regarding Grounds:

    I've done/created redundant grounds for the headlights, turn signals and brake lights.

    #1 Was This A Good Or Bad Idea?

    #2 My body will be coming off for paint soon so should I keep them or not?

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    Quote Originally Posted by GoDadGo View Post
    Steve's Stupid Questions Regarding Grounds:

    I've done/created redundant grounds for the headlights, turn signals and brake lights.

    #1 Was This A Good Or Bad Idea?

    #2 My body will be coming off for paint soon so should I keep them or not?
    Steve,

    More "solid" grounds can't hurt.

    At a minimum, the battery (-) needs a good chassis ground. The engine block needs a good ground to the chassis. The RF harness needs a good ground to the chassis.
    There are 10 types of people in this world;
    those who understand binary and those who don't.

    My Build Thread: http://thefactoryfiveforum.com/showt...ter-Build-9754

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  10. #7
    Boydster's Avatar
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    Quote Originally Posted by GoDadGo View Post
    Steve's Stupid Questions Regarding Grounds:

    I've done/created redundant grounds for the headlights, turn signals and brake lights.

    #1 Was This A Good Or Bad Idea?

    #2 My body will be coming off for paint soon so should I keep them or not?
    I also created multiple grounds. I have my lights grounded to chassis at each corner of the car, plus the harness ground. Only problem with too many grounds is the wires and the splices... IOW, do it.
    ---Boyd---
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    Last edited by davvet2; 10-03-2019 at 09:48 PM.

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    After a lot of testing and also trying a new switch I’ve narrowed it down to current somehow feeding from one input to the other at the LEDs. For example, when I have just the ground and flasher connected to either of the turn signal LEDs I read current coming back out on the other input for the LED (I.e. the running lights). I just switched everything except the headlights back over to the original lights and all works as it should so I don’t think wiring is an issue. I also added grounds at all four corners as suggested.

    Good to know I have a completely working solution but would really like to used the LEDs. Any thoughts?
    MKIV #9542 Complete Kit, Coyote, IRS - Delivered - 2/19/19, First start - 9/8/19, Go Cart - 9/14/19
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  13. #10
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    Did you switch the flasher relays over to non-resistive types that are compatible with LEDs? If that doesn't solve it, then you will need to install blocking diodes on the circuits that are back feeding.

    I used these on my turn signals: https://www.amazon.com/1N5824-SCHOTT...4&sr=8-2-fkmr0
    Last edited by Papa; 10-04-2019 at 06:26 PM.
    There are 10 types of people in this world;
    those who understand binary and those who don't.

    My Build Thread: http://thefactoryfiveforum.com/showt...ter-Build-9754

  14. #11
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    Quote Originally Posted by Papa View Post
    Did you switch the flasher relays over to non-resistive types that are compatible with LEDs? If that doesn't solve it, then you will need to install blocking diodes on the circuits that are back feeding.
    I installed two of these electronic flashers that came with the package from Watson’s.

    https://www.memotronics.com/2-prong-...2rlnp-bipolar/

    I may need to try the diode’s. Did you just put them on the flasher inputs or running lights as well?
    MKIV #9542 Complete Kit, Coyote, IRS - Delivered - 2/19/19, First start - 9/8/19, Go Cart - 9/14/19
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  15. #12
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    I installed them at the output of my turn signal switch, which is an SDC self-cancelling setup.

    There are 10 types of people in this world;
    those who understand binary and those who don't.

    My Build Thread: http://thefactoryfiveforum.com/showt...ter-Build-9754

  16. #13
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    What is the LED package from Watsons? Are you using the stock Factory Five tail lights or something different?

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    I bought the Basic Cobra LED Upgrade Package. https://watsons-streetworks.com/prod...grade-package/

    Mostly the same package you can get from Breeze. I didn’t realize Breeze sold a set as well.

    Thanks for the picture Papa! I have a couple extra diodes from putting together the Russ Thompson setup but will get a few more and put them in line on all the turn signal and running light leads.
    MKIV #9542 Complete Kit, Coyote, IRS - Delivered - 2/19/19, First start - 9/8/19, Go Cart - 9/14/19
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  18. #15
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    If you're wiring looks good, as it does, Led's can be a pain, but they should be simple.

    The electronic flasher units prevent hyper-flashing. If your flash rate is OK, it is OK.
    The diodes prevents a backfeed from one circuit to another. Usually used to separate the turn signal sides so they dont backfeed across the indicator or the switch, powering the opposite side and often leading to 4-way flashers when you engage the TS'es.

    when I have just the ground and flasher connected to either of the turn signal LEDs I read current coming back out on the other input for the LED (I.e. the running lights).
    If the running light power wire is disconnected from the rest of the car, ie: there is NO WAY the current is not coming from the dash, then obviously its coming through the LED and that is bad. You could even prove this on the bench.
    LEDs shouldnt do this and its an indication of an internal failure in the circuitry. But one more thing to look at is the way the contacts on the led unit are making in the socket. Make sure theres no little piece of stray solder and that the lamp is aligning correctly. Sometimes the led manufacturers use these elongated contacts, and if they are not aligned perfectly, they can short across and cause exactly what you are seeing.

    An all LED car is very possible and many have done it, including me. Just gotta find that detail thats messing you up.
    ---Boyd---
    MkIV #9042 build thread
    www.boss427.us
    Plan: 427W-X, TKO600, Moser 3.55 rear.
    Delivered Feb 2017. First start Oct 22, 2017.
    First go-cart Mar 26, 2018. Back from Whitby's paint Aug 17, 2019.
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  19. #16
    Senior Member edwardb's Avatar
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    I've done two builds with 100% LED lighting. #8674 with the package from Watson's Streetworks. Same as the package from Breeze. Re-sold as I understand. But mine was a few years ago, so no guarantee all the components are exactly the same. My Gen 3 Coupe build is also 100% LED lighting with parts from a variety of sources including Factory Five. Both builds have solid state flashers from Watson's and both builds work perfectly.

    Having said that, I guess I've been lucky. I've worked with several builders who have experienced various issues when switching to LED's. Once any wiring or ground issues were resolved, all traced to backfeeding within the LED devices themselves. If you do a Google search, you'll find this talked about in a number of forums across many interest groups. Typically this problem can be confirmed by replacing the LED's with incandescent one at a time and finding when the problem starts. Sometimes can be traced to a single device, or similar devices. I've heard of guys running incandescents in their front running lights and everything else LED. That seemed to have solved the problem for them. Adding one-way diodes into the offending lines, as described here, is another common solution. The challenge is to find where they're required.

    Whether solid state flashers are installed or not shouldn't be related to this problem. The issue there is LED's don't pull enough current to energize the traditional electromechanical flashers that work via a bi-metal strip and heat. So the failure mode if the flashers aren't changed is the lights don't flash. They go on but won't flash. Guys used to put load resistors in the line to draw enough current to flash the old style flashers. But that defeats one of the advantages of LED which is reduced current. Solid state flashers are a much more elegant solution and in theory should be more durable. They're also sealed, so don't get damaged by moisture or rainwater running down into the fuse panel. Ask me how I know about that.
    Last edited by edwardb; 10-05-2019 at 08:05 AM.
    Build 1: Mk3 Roadster #5125. Sold 11/08/2014.
    Build 2: Mk4 Roadster #7750. Sold 04/10/2017. #7750 Build Thread
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  20. #17
    Not a waxer Jeff Kleiner's Avatar
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    I haven't read all the replies so this is just a spitball---would reversed polarity on one or more of the LEDs play into this?

    Jeff

  21. #18
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    Woohooooo! It’s fixed!!!! Bench tested the LEDs and all were good. Went around one by one and replaced the regular bulbs with LEDs starting in the rear and all was good until the last one on the front drivers side turn signal. When I put the LED in and tried the turn signals with the headlights on it just stayed lit and when I tried the turn signal without the headlights it caused the other blinkers to lightly flash. Put a diode on the running light wire for the front drivers turn signal and all is now working as it should.

    Great feeling to get it working. Still not completely sure what is causing the bleed over on that leg of the wiring (I didn’t see it with the regular bulb in) but glad it works regardless.
    MKIV #9542 Complete Kit, Coyote, IRS - Delivered - 2/19/19, First start - 9/8/19, Go Cart - 9/14/19
    1965 Mustang Convertible 4v 289
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