Electrical Need help please! No spark, Fuel pump not priming, and a mystery wire.

Discussion in 'Fox 5.0 Mustang Tech' started by 15reidna, Mar 24, 2013.


  1. 7991LXnSHO

    7991LXnSHO Active Member

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    I nominate jrichker for a " favorite tool" of the year award for 2013 if he has room on the mantle!
    #21
    88LX5.Oh likes this.
  2. jrichker

    jrichker StangNet's favorite TOOL SN Certified Technician Founding Member

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    Thanks for the vote of confidence. It remains to be seen if the WunderKid (I wonder if this will fix it) will actually find and fix the problem...
    #22
  3. 15reidna

    15reidna New Member

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    Is the fuel pump relay coil the same thing as the relay under the drivers seat?
    #23
  4. 15reidna

    15reidna New Member

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    Alright hopefully the problem is the fuel pump relay coil but I don't know what the relay coil does, where it is, what it looks like, or how to fix it. Is it by the EEC?
    #24
  5. jrichker

    jrichker StangNet's favorite TOOL SN Certified Technician Founding Member

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    Do you have 12 volts on the red/green wire with the ignition switch in the Run position.? Yes/No
    #25
  6. 15reidna

    15reidna New Member

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    Just checked and I still don't have any voltage reading in the red/green wire in the ignition switch.
    #26
  7. jrichker

    jrichker StangNet's favorite TOOL SN Certified Technician Founding Member

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    Then replacing the fuel pump relay will not fix the problem.

    You MUST have 12 volts on the red/green wire with the ignition switch in the Run position for any part of the fuel system, ignition system or computer system to work properly.

    Accessing the ignition switch to test the voltages:
    There are 2 other screws in the lower dash cover that need to be removed
    [​IMG]
    [​IMG]
    [​IMG]
    [​IMG]
    The ignition switch is under the plastic cover on the steering column. There are 3 long screws that secure the top and bottom parts of the plastic cover. The screws are located in th bottom cover.

    Using the diagram below, look for 12 volts on the red/green wire with the ignition switch in the Run position. Measure it right at the switch.

    Diagram courtesy of Tmoss & Stang&2birds

    [​IMG]

    Good 12 volts on the red/green wire at the switch with the ignition switch in the Run position, then the switch is good.
    The problem is in the fuse link located in the wiring harness.

    No 12 volts at the red/green wire at the switch with the ignition switch in the Run position, then check the yellow wires going to the switch.

    Good 12 volts on the yellow wires, then replace the ignition switch.
    No 12 volts on the yellow wires, then the fuse link shown in the diagram above is blown open.

    See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host) for help on 88-95 wiring http://www.veryuseful.com/mustang/tech/engine/ Everyone should bookmark this site.

    Ignition switch wiring
    http://www.veryuseful.com/mustang/tech/engine/images/IgnitionSwitchWiring.gif

    Fuel, alternator, A/C and ignition wiring
    http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

    Complete computer, actuator & sensor wiring diagram for 88-91 Mass Air Mustangs
    http://www.veryuseful.com/mustang/tech/engine/images/88-91_5.0_EEC_Wiring_Diagram.gif

    Complete computer, actuator & sensor wiring diagram for 91-93 Mass Air Mustangs
    http://www.veryuseful.com/mustang/tech/engine/images/91-93_5.0_EEC_Wiring_Diagram.gif

    Vacuum diagram 89-93 Mustangs
    http://www.veryuseful.com/mustang/tech/engine/images/mustangFoxFordVacuumDiagram.jpg

    HVAC vacuum diagram
    http://www.veryuseful.com/mustang/tech/engine/images/Mustang_AC_heat_vacuum_controls.gif

    TFI module differences & pin out
    http://www.veryuseful.com/mustang/tech/engine/images/TFI_5.0_comparison.gif

    Fuse box layout
    http://www.veryuseful.com/mustang/tech/engine/images/MustangFuseBox.gif

    87-92 power window wiring
    http://www.veryuseful.com/mustang/tech/engine/images/mustang87-92 PowerWindowWiring.gif

    93 power window wiring
    http://www.veryuseful.com/mustang/tech/engine/images/mustang93PowerWindows.gif
    #27
  8. 15reidna

    15reidna New Member

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    I have no volts going to the red/green wire and I do have power to both yellow. I already replaced the ignition switch though so I don't think that its bad already. At this point I'm thinking that a mouse has chewed through a wire somewhere.
    #28
  9. 88LX5.Oh

    88LX5.Oh Advanced Member

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    So according to the diagram JR supplied you with, what you're saying is, you're getting power TO the ignition switch (big yellow wires are main power wires for switch), but you're not getting any power to the ignition coil. Is this correct?
    #29
  10. jrichker

    jrichker StangNet's favorite TOOL SN Certified Technician Founding Member

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    NO 12 volts on the red/green wire AT the ignition switch itself? Are you sure the switch is properly engaging the key lock mechanism?
    #30
  11. 15reidna

    15reidna New Member

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    Yes, No 12 volts to the red/green wire and I just checked the ignition coil and didn't get anything out of that either. Which is weird because the ignition coil is also brand new.
    #31
  12. jrichker

    jrichker StangNet's favorite TOOL SN Certified Technician Founding Member

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    You MUST have 12 volts on the red/green wire with the ignition switch in the Run position for any part of the fuel system, ignition system or computer system to work properly. It doesn't matter if it is a new part or an old part, no 12 volts on the red/green wire with the ignition switch in the Run position no worky, no matter what.

    If you do not have 12 volts AT the ignition switch with it in the Run position and DO have 12 volts on the yellow wire, then there are 3 possibilities:
    1.) You forgot to turn the ignition switch on, or did not turn it far enough to get it to the Run position.
    2.) The slider bar that moves the ignition switch isn't engaging the switch properly.
    3.) The ignition switch is defective or the parts house sold you the wrong switch.

    The correct ignition switch looks like this:

    [​IMG]

    [​IMG]

    [​IMG]


    Saleen0679 was nice enough to dig this up for us awhile back: Replace a 1979-1993 Ignition Switch Assembly
    #32
  13. 15reidna

    15reidna New Member

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    Just replaced all the fusable links with actual fusable links from autozone instead of just having them bipassed and wuala! She runs again and runs better then ever! Thanks for all your help!! I probably would have never found it without your help. Thanks.
    #33
  14. jrichker

    jrichker StangNet's favorite TOOL SN Certified Technician Founding Member

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    I am certainly glad to hear that you got it fixed. Enjoy your ride. :)
    #34

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