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  1. #1
    FEP Supporter vdubn's Avatar
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    Default Headlight Switch Acting Strangely

    I just got my car back together, after the inside and wiring had been gutted by the previous owner, so I am working through each electrical feature making sure that everything works as it should. The headlight switch is acting very strange. I have the stock headlight switch, connected to a harness that is relayed, so the harness connects to the drivers side hi/low headlight plug, and that harness is controlled by dual relays and connects to the headlights. When I turned the headlight switch on the first time, the parking lights came on, but no headlights. Then, if I switched the high beams on, the low beams came on, and when I shut the headlight switch off, the headlights stayed on for a minute, and eventually went off.

    My fog lights run off of the headlight switch as well, and no matter what, the fogs don't come on at all.

    I am thinking that I just need a new headlight switch, but thought it strange that no matter what I couldn't get hi beam lights to work, and low beams only came on if I switched the stalk to the high beam setting.

    Thanks in advance for any suggestions.
    85 GT Hatchback, T-Tops. Rebuilt 302, 10.6:1, Edelbrock Alum heads, Performer Intake, full EFI swap from 86, 3.73 Posi 8.8, 5 lug Cobra 13" fr and 12.6" rear disc swap, MM SubFrame Connectors, MM Panhard Bar, MM front A-Arms, MM rear control arms, Raceland Coilovers, T5 with Centerforce DF Clutch.

  2. #2
    FEP Supporter 4-barrel Mike's Avatar
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    Default

    Sounds like bad grounds.

    Mike
    1985 ascMcLaren 5.0 SC Roadster
    My '78 Fairmont build - http://vb.foureyedpride.com/showthre...539-78-Big-Red

  3. #3
    FEP Supporter vdubn's Avatar
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    I agree that it sounds like a ground, but I added 2 extra grounds, both 2-gauge wire, plus all of the factory grounds, and I made sure all had clean fresh connections to bare metal. I will check and see if I may have left one of the mounting bolts loose, but I doubt it. I have heard of the factory high beam relay that is built into the headlight switch causing strange behavior, so I thought maybe it was that.
    85 GT Hatchback, T-Tops. Rebuilt 302, 10.6:1, Edelbrock Alum heads, Performer Intake, full EFI swap from 86, 3.73 Posi 8.8, 5 lug Cobra 13" fr and 12.6" rear disc swap, MM SubFrame Connectors, MM Panhard Bar, MM front A-Arms, MM rear control arms, Raceland Coilovers, T5 with Centerforce DF Clutch.

  4. #4
    Moderator wraithracing's Avatar
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    Default

    Can you power the lights individually with something like a Power Probe? If so, I would test and see what happens with that. If everything works, then either you have a bad headlight switch or something in the wiring from the switch to your relays is messed up.

    Bad grounds are always a possibility, but if you can test each circuit without the switch and they work, then grounds are most likely not your issue. Good Luck!
    ​Trey

    "I Don't build it hoping for your approval! I built it because it meets mine!"

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  5. #5
    FEP Supporter 4-barrel Mike's Avatar
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    Headlight grounds good?
    1985 ascMcLaren 5.0 SC Roadster
    My '78 Fairmont build - http://vb.foureyedpride.com/showthre...539-78-Big-Red

  6. #6

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    if I had to guess, headlight hi/low dimmer switch failed. Get a Dvom or a test light at bare minimum and start checking the circuits.
    84 LX Vert. 5.0 5speed canyon red on white
    99 cobra, electric green on medium parchment, vortech s-trim

  7. #7
    FEP Supporter vdubn's Avatar
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    Quote Originally Posted by Lowetlx View Post
    if I had to guess, headlight hi/low dimmer switch failed. Get a Dvom or a test light at bare minimum and start checking the circuits.
    Funny you mention that, as I had another member say that as well. Apparently all voltage goes through the dimmer stalk, which I didn't realize.
    85 GT Hatchback, T-Tops. Rebuilt 302, 10.6:1, Edelbrock Alum heads, Performer Intake, full EFI swap from 86, 3.73 Posi 8.8, 5 lug Cobra 13" fr and 12.6" rear disc swap, MM SubFrame Connectors, MM Panhard Bar, MM front A-Arms, MM rear control arms, Raceland Coilovers, T5 with Centerforce DF Clutch.

  8. #8

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    Is your car equipped with headlight auto-dim and/or headlight shutoff delay? That can add some complexity.

  9. #9
    FEP Supporter vdubn's Avatar
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    I don't think that our cars had those as options back in 1985/86, but I could be wrong.
    85 GT Hatchback, T-Tops. Rebuilt 302, 10.6:1, Edelbrock Alum heads, Performer Intake, full EFI swap from 86, 3.73 Posi 8.8, 5 lug Cobra 13" fr and 12.6" rear disc swap, MM SubFrame Connectors, MM Panhard Bar, MM front A-Arms, MM rear control arms, Raceland Coilovers, T5 with Centerforce DF Clutch.

  10. #10
    FEP Member Tigger's Avatar
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    Did you repin in the lower beam headlight plug when you installed the H4’s?

    When I installed my Hella’s the first time I just took the old bulbs out and plugged the Hella’s in. The headlights did something weird like yours are doing. I don’t remember exactly as it was two years ago but they did not work right. I found out that you have to repin the lower beam plug. There is a thread I found here on the site that explained it.

    I have driven my car very little in the dark since I installed them. They are tons brighter than the regular bulbs but i think I need to change out the original headlight switch and do the relay mod because the high beams can only stay on for a minute or two before the headlight switch relay starts wigging out. Driving with just the low beams on are not a problem yet. I am interested to know how well your setup works. There were a couple good write ups I found to add the relays but now that photobucket did what they did they are no longer detailed.
    67 Mustang Coupe
    96 Tangerine GT
    86 Saleen #179

  11. #11
    FEP Supporter vdubn's Avatar
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    So I got the H4 bulbs, along with a full harness with 2 relays. I went ahead and just plugged the harness into the drivers side headlight hi/lo plug. Maybe the issue you are describing is what I am running into. If you can find the other article, that would be really helpful.
    85 GT Hatchback, T-Tops. Rebuilt 302, 10.6:1, Edelbrock Alum heads, Performer Intake, full EFI swap from 86, 3.73 Posi 8.8, 5 lug Cobra 13" fr and 12.6" rear disc swap, MM SubFrame Connectors, MM Panhard Bar, MM front A-Arms, MM rear control arms, Raceland Coilovers, T5 with Centerforce DF Clutch.

  12. #12
    FEP Supporter vdubn's Avatar
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    Is this the article you mentioned, post number 5? I had no idea that the ground wire was on a different side of the headlight switch. Definitely could be the source of my issue. I will check tonight:

    http://vb.foureyedpride.com/showthre...77#post1286877
    85 GT Hatchback, T-Tops. Rebuilt 302, 10.6:1, Edelbrock Alum heads, Performer Intake, full EFI swap from 86, 3.73 Posi 8.8, 5 lug Cobra 13" fr and 12.6" rear disc swap, MM SubFrame Connectors, MM Panhard Bar, MM front A-Arms, MM rear control arms, Raceland Coilovers, T5 with Centerforce DF Clutch.

  13. #13
    FEP Member Tigger's Avatar
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    Here you go, this is what my Saleen did. I re-pinned the plug and they work just fine other than the switch is bad.

    http://vb.foureyedpride.com/showthre...H4-Weird-Issue
    67 Mustang Coupe
    96 Tangerine GT
    86 Saleen #179

  14. #14
    FEP Member Tigger's Avatar
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    Different thread but same diagram from FoxChassis
    67 Mustang Coupe
    96 Tangerine GT
    86 Saleen #179

  15. #15
    FEP Supporter vdubn's Avatar
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    Ok, so I switched the wires around, and now I get hi beams when I hit my hi beam switch, but now when I turn the headlight switch on, I get no low beams. I wonder if I toasted the switch, or ???

    One other cool side affect, my passenger side fog light works, (I had not fogs before) and the light on the fog switch is on. Neither worked when the headlight harness was wired backwards. I need to see if I have voltage at the drivers side fog light, and am hoping that the fogs are good to go now, just a connection issue hopefully.
    85 GT Hatchback, T-Tops. Rebuilt 302, 10.6:1, Edelbrock Alum heads, Performer Intake, full EFI swap from 86, 3.73 Posi 8.8, 5 lug Cobra 13" fr and 12.6" rear disc swap, MM SubFrame Connectors, MM Panhard Bar, MM front A-Arms, MM rear control arms, Raceland Coilovers, T5 with Centerforce DF Clutch.

  16. #16
    FEP Supporter vdubn's Avatar
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    I also just noticed that when I hit my left turn signal, the outside bulbs blink, but pretty slow, and the dash turn light doesn't light (guessing the dash bulb would help fix that). If I switch to the right side, the bulb in the dash lights, but won't blink, and the rear bulb doesn't light up.

    I have all new bulbs throughout the car, so its not a bulb issue.
    85 GT Hatchback, T-Tops. Rebuilt 302, 10.6:1, Edelbrock Alum heads, Performer Intake, full EFI swap from 86, 3.73 Posi 8.8, 5 lug Cobra 13" fr and 12.6" rear disc swap, MM SubFrame Connectors, MM Panhard Bar, MM front A-Arms, MM rear control arms, Raceland Coilovers, T5 with Centerforce DF Clutch.

  17. #17
    FEP Member Tigger's Avatar
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    How are the hazards? If it is blinking slow the blinker relay might need replaced.
    67 Mustang Coupe
    96 Tangerine GT
    86 Saleen #179

  18. #18
    FEP Member Tigger's Avatar
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    One other thought is to take the relay harness out(if it is not too much trouble) and just plug in the bulbs to the factory wiring and see if everything works?
    67 Mustang Coupe
    96 Tangerine GT
    86 Saleen #179

  19. #19
    FEP Supporter vdubn's Avatar
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    I just tried the 4 way flashers, and all outside lights work except for the right rear. I will check that bulb/socket tomorrow and will replace a few bulbs that are out in the dash, one of which is the left turn signal. I'll see if the flasher works better with all bulbs working. If its still slow, then I'll bet you are correct on the flasher possibly being bad.
    85 GT Hatchback, T-Tops. Rebuilt 302, 10.6:1, Edelbrock Alum heads, Performer Intake, full EFI swap from 86, 3.73 Posi 8.8, 5 lug Cobra 13" fr and 12.6" rear disc swap, MM SubFrame Connectors, MM Panhard Bar, MM front A-Arms, MM rear control arms, Raceland Coilovers, T5 with Centerforce DF Clutch.

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