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Thread: Speed control drops out after a feww sec when headlights are on.

  1. #1

    Default Speed control drops out after a feww sec when headlights are on.

    Any ideas?
    84 Town Car.

    It must be electrical.

    Brake/turn signal light circuit had been modified to meet german laws that require a amber turn signal.
    The two bulbs per light assembly had been spearated into one for turn signal only and the other for park/brake by splicing the wires and runnig a separate brake wire to the lamps.

    Speed control did not work when I bought the car due to this modification. They had clipped and the green and green/red brake switch wires but they are mandatory for speed control operation. I traced that down to the switch wiring and after resoldering the wire I had speed control again.
    But only when headlights are off.

    I assume the dropping out of speed control after a few seconds of keeping must have something to do with the rear lights.

  2. #2
    GMN Regular DerekTheGreat's Avatar
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    Yah, I'm not an electrical guru but it seems as if they spliced or used the factory wire for the brake lights for whatever modification. So, when you turn your lights on the cruise module or whatever "sees" that the brakes are applied, thus killing cruise.
    1985 LTD Crown Victoria - SOLD
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  3. #3
    Beater gonna beat sly's Avatar
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    under dash grounds... if they're starting that insulation shrinking fraying business... that could be the issue. May also need to check the power lead to the cruise control module for the same issue.

    Only two things are infinite, the universe and human stupidity, and I'm not sure about the former. -- Albert Einstein
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  4. #4
    I'm an air-conditioned gypsy gadget73's Avatar
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    Check the grounds for your tail lights. The cruise control has to "see" ground through the brake lamps in order to be on. Thats why it drops out when you step on the brake. It doesn't actually look for +12v, it just looks for no ground. If the ground connection in the trunk for the lights (pretty sure its driver's side, near the trunk hinge) is bad, it will ground through the parking lamps if they are off. If the lamps are on, no ground, no cruise.

    86 Lincoln Town Car (Galactica).
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  5. #5

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    Thanks, Iīll check grounds.

  6. #6

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    I checked grounds. They are ok. Even cleaned them to be sure.

    I observed the following:
    When tail lights are ON and you look closely you can see the brake/turn light filaments to flicker very slightly. Thatīs why it drops out of speed control since the amplifier "sees" ground via the filament.
    BUT WHY do they flicker?

    Pulled headlight switch and cleaned spade connectors. One had minimal oxidation. Still not better. No auto dim or delay btw. Plain switch.

    I also noticed that any time I reconnect the battery ground and turn on the taillights the brake/turn lights fully light up for about 10 seconds, then drop to the slight flicker mode. Whatīs ging on here? Thatīs definitely not normal.

  7. #7
    Beater gonna beat sly's Avatar
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    If the brake filament is getting intermittent signal, you may have to adjust the brake switch to be "more off" or replace the brake switch. I'd say check the high mount brake light, but I don't think those were a thing until later. That would let you know if that's coming from the brake switch or the multifunction switch. I don't see how the multifunction switch would back-feed the brake circuit, but it might be possible.

    Only two things are infinite, the universe and human stupidity, and I'm not sure about the former. -- Albert Einstein
    rides: 93 Crown Vic LX (The Red Velvet Cake), 2000 Crown Vic base model (Sandy), 2003 Expedition (the vacation beast)
    Quote Originally Posted by gadget73
    ... and it should all work like magic and unicorns and stuff.
    Quote Originally Posted by dmccaig
    Overhead, some poor bastards are flying in airplanes.

  8. #8
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    Replace the brake switch. It might look good, but they go bad. A new switch is not expensive, just get a good brand.

  9. #9

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    Apparently I have one spare from my 84 F250. Iīll try it.
    But the flicker is only with lights on. Not when they are off.

    Too bad that the multifunction switch is not easily acessible for spray cleaning.

  10. #10
    P31 Pursuit Car Brown_Muscle's Avatar
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    If the brake light switch doesn't work... Could one of the brake light filaments be touching the other filaments that come on with the headlights and sporadically back-feed power into the brake light circuit?
    -Phil



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  11. #11

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    Still flickers with brake switch disconnected.
    I noticed that the insturment cluster, ATC and ashtray lights also flicker in sync with the brake lights. But not every time.
    Yesterday I had the flicker on one way. When returning they did not flicker once - cruise worked all the way when the lights were steady of course.

    Sometimes when starting the car the dash illumination flickers up and then goes out after a few seconds. And that is with lights OFF! Just after starting the car.
    I believe this is a hint to the whole issue. But donīt know where to hunt for.

  12. #12
    Lost and driftin' Arquemann's Avatar
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    I know it might be a long shot, but make sure the voltage regulator is working correctly.
    You most likely have an intermittent short somewhere in the power distribution. Or a bad ground, but you've checked those in the engine bay atleast...
    1985 Mercury Grand Marquis LS, "Maisa"
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  13. #13
    GMN Regular DerekTheGreat's Avatar
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    Yah, I was going to ask if any of the flickering occurs with the engine off..
    1985 LTD Crown Victoria - SOLD
    1988 Town Car Signature - Current Party Barge

  14. #14

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    Yup, no matter if engine off or on - flickers. But like I said not everytime.
    Regulator is still from 1984. I definitely gotta check the connector for oxidation and ground at the housing.
    how would I know itīs defective?

  15. #15

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    PO had installed a new alternator. Could it be that my regulator needs terminals jumpered momentarily for a reset? My ī56 Cadillac needs that to be done anytime the generator is disconnected from the harness but I know that generator and alternators are different. So maybe Iīm wrong in my guess.

  16. #16
    Lost and driftin' Arquemann's Avatar
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    I don't think there's any reset procedure for the voltage regulator, your caddy has some wonky 50's tech lol.
    All I can say for testing the regulator is to check battery voltage especially on startup and higher revs.

    Now that you mentioned the lights flickering even with the engine OFF, I would suspect a short even more.
    Is there any constant behaviour with the flickering? Can you stop it in any way, shutting off the car, toggling lights on/off. Does the flickering last as long every time? If you disconnect the battery during the flickering and reconnect it, does it contiinue?
    1985 Mercury Grand Marquis LS, "Maisa"
    2008 BMW 530d Touring, "Femma"

  17. #17
    Beater gonna beat sly's Avatar
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    No reset procedure. It's super stupid regulator. It should just work or not. Cleaning contacts might be a good idea. Checking chassis ground, cables are tight in the terminals, wires are not green/damaged, etc.

    Only two things are infinite, the universe and human stupidity, and I'm not sure about the former. -- Albert Einstein
    rides: 93 Crown Vic LX (The Red Velvet Cake), 2000 Crown Vic base model (Sandy), 2003 Expedition (the vacation beast)
    Quote Originally Posted by gadget73
    ... and it should all work like magic and unicorns and stuff.
    Quote Originally Posted by dmccaig
    Overhead, some poor bastards are flying in airplanes.

  18. #18
    I'm an air-conditioned gypsy gadget73's Avatar
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    Generators need to be polarized before they work, the usual method is to apply battery voltage to the field coil, which can be done by jumping the regulator. This typically only needs to happen when the generator is new, they don't de-polarize from being unhooked. There isn't a "reset" function in any of this stuff. No computer, no memory, etc.

    If you're getting flickering lights without the engine running you have some wiring gremlin. Was this modified for EU lighting standards? If so I'd probably have a look at what exactly they did because its possible something is wrong.

    Voltage reg related stuff is a pulsing voltage while the engine is running only. The regulator only controls alternator output, if the engine isn't running there is nothing to control.

    86 Lincoln Town Car (Galactica).
    5.0 HO, CompCams XE258,Scorpion 1.72 roller rockers, 3.55 K code rear, tow package, BHPerformance ported E7 heads, Tmoss Explorer intake, 65mm throttle body, Hedman 1 5/8" headers, 2.5" dual exhaust, ASP underdrive pulley

    91 Lincoln Mark VII LSC SE, triple black (Timewarp) - poly front bushings, KYB struts and shocks, Holley SystemMax1 lower intake, SilverFox AOD valve body,

    1984 Lincoln Continental TurboDiesel - rolls coal

    Quote Originally Posted by phayzer5 View Post
    I drive a Lincoln. I can't be bothered to shift like the peasants and rabble rousers

  19. #19
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    Lights flickering with key off to me says headlight switch. Headlight switch gets 12v all the time.
    I know you said you cleaned it but headlight switches get used a lot and they do wear out. I went through this in my fox, and used a multimeter to test the switch, and the switch was worn. Was not carrying the proper voltage through all of the circuits.
    Since other lights on the same circuit are responding the same way, i would suspect the power feed to the headlight switch, or the switch itself. Not sure if your headlight switch has its own separate ground.
    Chances of every other power wire going from the headlight switch to all of the other lights going bad simultaneously is not high, which is why grounds were suggested.
    Chances of every ground associated with the lights being bad is also not high. Plus you checked them so that should be fine.
    What is the common denominator?
    The headlight switch.
    Plus you said the cruise works with headlights off.
    Either the switch is bad or the wiring to the switch is bad in my opinion.
    I would start there and test out the headlight switch.

    You said someone else was in there and modified the wiring already, so it might be worthwhile to test everything out.
    Those era Fords get headlight power from the starter solenoid but i might be wrong.
    ..

  20. #20

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    I had suspected the headlight switch, too since itīs the common denominator. Thatīs why I cleaned the connector and flooded the switch with radio tuner spray. Will have to test the terminals like the troubleshooting manuals shows.

    Yes. the rear brake/turn wiring was modified to meet EU lighting standards.
    I.e.:
    The double bulb rear lights with both top and bottom bulbs acting simultanely as tail and brake/turn lights was separated into the upper being turn only (tail light wire clipped) and the bottom being tail and brake only. They had run new turn and brake wires from the front to the rear. This makes no sense to me. They couldīve kept the stock turn wires and ran one new brake wire only. Anyway. I had to resolder both green and green/red hash wires to the brake switch to get working cruise. They had clipped these, too and ran the new brake wire directly from power to the brake switch, omitting the whole multifunction switch and cruise amplifier system. Thatīs why speed control didnīt work in the beginning at all.
    I have restored the wiring up front back to stock. I have kept the two new wires (brake and turn) and the separate bulb housings circuits for turn /brake/tail.

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