Electrical Electrical Gremlins -- Help!!!! Please

Discussion in 'Fox 5.0 Mustang Tech' started by MAB, Jul 29, 2014.


  1. MAB

    MAB New Member

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    1987 LX 5.0 air conditioner and turn signals work with key on, as soon as I start the car they wont work.

    When I turn the hazard lights on with car off it causes the temperature gauge to rise with each hazard flash, it rises all the way to the top until you cant see it anymore. Anyone????????
     
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    Last edited by a moderator: Aug 3, 2014
  2. rbohm

    rbohm Founding Member

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    start by making sure you have the engine grounded to the chassis. bad grounds cause more electrical issues than anything else.
     
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  3. Spaz

    Spaz Member

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    Next thing after grounds that cause a lot of electrical problems is the ignition switch. Has yours ever been changed? If not it is most likely falling apart.
     
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  4. jrichker

    jrichker StangNet's favorite TOOL SN Certified Technician Founding Member

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    Two problems: Ignition switch and bad secondary power ground...

    Recall on Ford Ignition switches:
    Some of the symptoms of ignition switch problems are things that don’t work or are intermittent like radio, turn signals, wipers or heater.

    There was a FREE recall on Ford ignition switches. They overheat and sometimes catch fire. That burns up the steering column and sometimes the car interior. Since this is very old information, you may not be able to get the switch replaced for free anymore. The auto parts stores sell the switches for $13-$15.

    [​IMG]

    [​IMG]

    [​IMG]

    Saleen0679 was nice enough to dig this up for us awhile back: Replace a 1979-1993 Ignition Switch Assembly





    See item #2 for the secondary power ground...
    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.

    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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  5. MAB

    MAB New Member

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    Replaced the ignition switch and that fixed everything!!! Thank you very much!!! When the flashers are on with car off the temp gauge very slightly jumps. I will clean the grounds as stated in #2 above.
    Thanks again!
     
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  6. Noobz347

    Noobz347 Stangnet Facilities Maint Tech... Er... Janitor Admin Dude

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    On a side note:

    Your post was riddled with commercial links to various web sites. I have removed them. You should download and run a program called MalwareBytes.

    The link is here: http://www.malwarebytes.org/

    I've also renamed your thread so that folks know what the subject of your problem is.

    Good to see that you've found your solution.
     
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  7. mikestang63

    mikestang63 Mustang Master

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    In safe mode with no network run Smitfraudfix as well to clean up your computer. If you don't have a good anti virus, a good free one is AVG. I also recommend you run Spybot once a week.
     
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