Headlight Flicker After Pigtail Replace

Discussion in '1994 - 1995 Specific Tech' started by Dacon, Jul 24, 2014.

  1. Dacon

    Dacon Member

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    Bought a sn95 ('94) and realized it has the headlight flicker.

    Out with the old, in with a new pigtail with slightly thicker gauge wire. The old one was burned so bad it cracked and had a huge hole.

    Went for a drive (at night, lol) to test it. The flicker is still there, but it is less severe, but it is annoying. Is it possible it was left arcing so long the switch is slightly fouled? Would a new headlight switch with my harness fix my problem, or is it worse than that if it flickers after a pigtail replace ?
     
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  2. Dacon

    Dacon Member

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    A little reading some folks have had to replace the multi function switch to fix their issues, after replacing a fried pigtail.

    My question is, is replacing the headlight switch gonna make a difference ? My pigtail connector was fried bad (http://imgur.com/MWNwK1m ) but the connector on the headlight switch where it fried the pigtail looks clean, free of oxidation. Should I just replace the multi function switch and hope that works ?
     
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  3. toyman

    SN Certified Technician

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    I'll bet if you remove the headlight switch you will see that it has overheated and is cracked and/or broken.
     
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  4. stangr5oh

    stangr5oh Active Member

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    Or you have a intermitten ground problem. I would trace your headlight wiring from one end to the other and see if there is another fouled area or broken ground.
     
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    Last edited: Aug 10, 2014
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  5. Dacon

    Dacon Member

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    Picked up a switch, will pop it in tomorrow to see if it works. Do not feel like taking off the upper dash to track wires :(
     
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  6. toyman

    SN Certified Technician

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    Speaking of grounds. There are many component to chassis grounds. These connections generally stay secure. However, the battery to engine and engine to chassis grounds do corrode and need to be removed and cleaned. If these two are well maintained a host of operating issues will disappear. Every sensor requires a solid ground with it's origin back to the chassis.
     
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  7. Dacon

    Dacon Member

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    I am completely in the dark about a lot, electrical is one of them.

    The battery to engine/engine to chassis ground will just be wires connect from point to point? I've read the engine to chassis is near the motor mount, where is the battery to engine ground connected to on the battery ? Near the posts or ?
     
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  8. jrichker

    jrichker StangNet's favorite TOOL
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    Grounds

    Revised 28-Oct-2012 to add signal ground description & possible problems if it is bad

    Grounds are important to any electrical system, and especially to computer controlled engines. In an automobile, the ground is the return path for power to get back to the alternator and battery.

    Make sure that all the ground places are clean and shiny bare metal: no paint, no corrosion.

    1.) The main power ground is from engine block to battery: it is the power ground for the starter & alternator.


    2.) The secondary power ground is between the back of the intake manifold and the driver's side firewall. It is often missing or loose. It supplies ground for the alternator, A/C compressor clutch and other electrical accessories such as the gauges. The clue to a bad ground here is that the temp gauge goes up as you add electrical load such as heater, lights and A/C.

    Any car that has a 3G or high output current alternator needs a 4 gauge ground wire running from the block to the chassis ground where the battery pigtail ground connects. The 3G has a 130 amp capacity, so you wire the power side with 4 gauge wire. It stands to reason that the ground side handles just as much current, so it needs to be 4 gauge too.

    The picture shows the common ground point for the battery , computer, & extra 3G alternator ground wire as described above in paragraph 2. A screwdriver points to the bolt that is the common ground point.

    The battery common ground is a 10 gauge pigtail with the computer ground attached to it.
    Picture courtesy timewarped1972
    [​IMG]

    Correct negative battery ground cable.
    [​IMG]

    3.) The computer's main power ground (the one that comes from the battery ground wire) uses pins 40 & 60 for all the things it controls internally: it comes off the ground pigtail on the battery ground wire. Due to its proximity to the battery, it may become corroded by acid fumes from the battery.
    In 86-90 model cars, it is a black cylinder about 2 1/2" long by 1" diameter with a black/lt green wire.
    In 91-95 model cars it is a black cylinder about 2 1/2" long by 1" diameter with a black/white wire.
    You'll find it up next to the starter solenoid where the wire goes into the wiring harness.

    All the grounds listed in items 1,2 & 3 need to bolt to clean, shiny bare metal. A wire brush or some fine sandpaper is the best thing to use to clean the ground connections.


    4.) All the sensors have a common separate signal ground. This includes the TPS, ACT, EGR, BAP, & VSS sensors. This ground is inside the computer and connects pin 46 to pins 40 & 60, which are the main computer grounds. If this internal computer ground gets damaged, you won't be able to dump codes and the car will have idle/stall/ performance problems

    5.) The O2 sensor heaters have their own ground (HEGO ground) coming from the computer. This is different and separate from the O2 sensor ground. It is an orange wire with a ring terminal on it. It is located in the fuel injector wiring harness and comes out under the throttle body. It gets connected to a manifold or bolt on back of the cylinder head.

    6.) The TFI module has 2 grounds: one for the foil shield around the wires and another for the module itself. The TFI module ground terminates inside the computer.

    7.) The computer takes the shield ground for the TFI module and runs it from pin 20 to the chassis near the computer.


    See http://assets.fluke.com/appnotes/automotive/beatbook.pdf for help for help troubleshooting voltage drops across connections and components. Be sure to have the maximum load on a circuit when testing voltage drops across connections. As current across a defective or weak connection, increases so does the voltage drop. A circuit or connection may check out good with no load or minimal load, but show up bad under maximum load conditions. .

    Voltage drops should not exceed the following:
    200 mV Wire or cable
    300 mV Switch
    100 mV Ground
    0 mV to <50 mV Sensor Connections
    0.0V bolt together connections

    [​IMG]

    Extra grounds are like the reserve parachute for a sky diver. If the main one fails, there is always your reserve.

    The best plan is to have all the grounds meet at one central spot and connect together there. That eliminates any voltage drops from grounds connected at different places. A voltage drop between the computer ground and the alternator power ground will effectively reduce the voltage available to the computer by the amount of the drop.
     
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  9. Dacon

    Dacon Member

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    Wow thanks.

    Still hoping the headlight switch eliminates the need tomorrow, but Ill clean 'em up to be sure!
     
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  10. Dacon

    Dacon Member

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    Hate to self bump, but the headlight switch fixed it.

    Odd thing is the old one didn't appear cracked, frayed, oxidized or anything. Some of the connector pins where it attaches to the plastic housing looked a little small/barely there (from factory), but the new switch has my lights very bright (I thought they were just dim being an old car!) and no more flickering. Thanks for the leads, time to clean the grounds for the hell of it now.
     
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  11. stangr5oh

    stangr5oh Active Member

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