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  1. #1
    FEP Member vdubn's Avatar
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    Default Large Yellow Wire (10 or 12 gauge), end of 1986 headlight harness, Where to Connect

    I have been scouring the wiring harnesses, and can find a solid yellow wire that feeds constant 12v to the starter, fuel pump, rear defrost, etc., but in my headlight harness, by where the alternator section is, has one 10 or 12 gauge single spade connector (grey plastic connector) on it. I figured that it might connect to the alternator, but don't see a spade connection for it. I also thought that maybe it connects to the starter, but also don't see a spade connection where this would go.

    I am connecting all of my engine bay harnesses, and just trying to figure out where this actually connects. I am guessing it needs a constant 12v, and can shorten or add an eyelet connector to it, but would prefer to leave stock if possible.

    I have checked for pics of engine harnesses, starter connections, alternator connections, etc., and I cannot find anything that shows a single spade connector attached to a 10ga or 12ga wire.

    Any guidance would be greatly appreciated.
    85 GT Hatchback, T-Tops. 2012 Coyote 5.0L Swap, T56 Magnum, GT550 Dept of Boost kit, with Eaton M122 SC, RAM 11" Powergrip clutch, BBK Long Tubes/OR X-Pipe, Flowmaster Axle Back, Stifflers DS Loop, and Rear X-member, AJE Tube Crossmember with AJE-Mod Mounts, 3.73 Posi 8.8, 5 lug Cobra 13" fr and 12.6" rear disc swap, 2004 Hydroboost Swap, MM SubFrame Connectors, MM Panhard Bar, MM front A-Arms, MM rear control arms, MM CC Plates, MM Coilovers w/Koni dampeners, MM Torque Arm (soon to be installed).

  2. #2
    FEP Member vdubn's Avatar
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    So I am thinking that the yellow wire should just connect to the stud on the back of the 130A alternator, just by mere proximity if nothing else, but have been confused by the fact that I haven't seen in any wiring diagrams where a large yellow wire connects to the back side of the alternator, especially with a spade connection. This yellow wire is taped with the other two alternator plugs (regulator and the black 2 wire plug), so it makes sense, but I would need to cut off the space connector and crimp on an eyelet, which isn't a big deal, I am just trying to understand how it must have worked on the 86 alternator that this harness was connected to.

    Here are some pics to give a reference.... granted, I am converting over to the 130A alternator as well, but I don't think that should matter, as I am just trying to figure out how this yellow wire was connected originally.

    Name:  alternatorwiring1.jpg
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    Name:  alternatorwiring2.jpg
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    85 GT Hatchback, T-Tops. 2012 Coyote 5.0L Swap, T56 Magnum, GT550 Dept of Boost kit, with Eaton M122 SC, RAM 11" Powergrip clutch, BBK Long Tubes/OR X-Pipe, Flowmaster Axle Back, Stifflers DS Loop, and Rear X-member, AJE Tube Crossmember with AJE-Mod Mounts, 3.73 Posi 8.8, 5 lug Cobra 13" fr and 12.6" rear disc swap, 2004 Hydroboost Swap, MM SubFrame Connectors, MM Panhard Bar, MM front A-Arms, MM rear control arms, MM CC Plates, MM Coilovers w/Koni dampeners, MM Torque Arm (soon to be installed).

  3. #3
    FEP Power Member tonysilver82's Avatar
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    Default

    That's for cars with rear defrost I think

  4. #4
    FEP Member vdubn's Avatar
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    I see where that is referenced in a bunch of google searches for this, but when I checked continuity, this wire is connected to the fuseable links that connect to the starter solenoid. Also, why would they run that wire for the rear defrost all the way over to the alternator, is it just to get direct current for running the rear defroster?

    Any reason why I shouldn't put an eyelet on this and connect it to the alternator?
    85 GT Hatchback, T-Tops. 2012 Coyote 5.0L Swap, T56 Magnum, GT550 Dept of Boost kit, with Eaton M122 SC, RAM 11" Powergrip clutch, BBK Long Tubes/OR X-Pipe, Flowmaster Axle Back, Stifflers DS Loop, and Rear X-member, AJE Tube Crossmember with AJE-Mod Mounts, 3.73 Posi 8.8, 5 lug Cobra 13" fr and 12.6" rear disc swap, 2004 Hydroboost Swap, MM SubFrame Connectors, MM Panhard Bar, MM front A-Arms, MM rear control arms, MM CC Plates, MM Coilovers w/Koni dampeners, MM Torque Arm (soon to be installed).

  5. #5
    FEP Power Member 4-barrel Mike's Avatar
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    The "occasionally reliable" internet shows that 8-gauge is good for ~55-60 amps (10-gauge less). If I remember correctly, my 3G alternators have double 6-gauge feeds.

    If you're planning on really using your 130A alternator, fab something bigger. Ace @185th & TV Highway should have everything you need very reasonably.

    Of course, YMMV :-)

    Mike

  6. #6
    FEP Member vdubn's Avatar
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    Quote Originally Posted by tonysilver82 View Post
    That's for cars with rear defrost I think
    Ok, I just figured out the mystery. I haven't found this information anywhere, even after knowing what I was looking for. No pics of this harness, nothing.

    Tony, you were correct, its the voltage feed for the rear defrost, and power travels from the drivers side of the car, through the headlight harness, through the fusable link connected at the starter solenoid, then travels to the front left by the headlights, across the radiator core support, and around the corner of the passengers side headlight area, and then back to the strut tower, where there is a grey connector that connects to a sub-harness that is just one yellow 12 gauge wire, and it goes through a separate firewall grommet, and connects to the dash harness on the passenger side, that goes to the defrost switch.

    Holy crap! What a path to send out to the engine compartment all the way around and back into the dash.... Since I was still using the dash harness out of my 85, the connector on the passenger side of the dash was grey, but in 1986 that connector changed to blue, which threw me off. I just happened to find a blue male version of this connector, and it happened to have the firewall grommet still on it, but the connector at the strut housing was wrapped in electric tape, so I passed it over probably a dozen times.

    Here are the pics showing the path backwards from the passenger side:

    Name:  defrostwiring1.jpg
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    Now after I swapped out the 86 connector:

    Name:  defrostwiring3.jpg
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    Here is a pic of the sub harness with the firewall grommet still attached:

    Name:  defrostwiring2.jpg
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    And finally, here is a pic of the connector that connects to the yellow wire that I almost cut off the end of, and connected to the alternator... that would have created a circular voltage loop...not sure how that would have worked, but thankfully I avoided it.

    Name:  defrostwiring4.jpg
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    85 GT Hatchback, T-Tops. 2012 Coyote 5.0L Swap, T56 Magnum, GT550 Dept of Boost kit, with Eaton M122 SC, RAM 11" Powergrip clutch, BBK Long Tubes/OR X-Pipe, Flowmaster Axle Back, Stifflers DS Loop, and Rear X-member, AJE Tube Crossmember with AJE-Mod Mounts, 3.73 Posi 8.8, 5 lug Cobra 13" fr and 12.6" rear disc swap, 2004 Hydroboost Swap, MM SubFrame Connectors, MM Panhard Bar, MM front A-Arms, MM rear control arms, MM CC Plates, MM Coilovers w/Koni dampeners, MM Torque Arm (soon to be installed).

  7. #7
    FEP Member vdubn's Avatar
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    Quote Originally Posted by 4-barrel Mike View Post
    The "occasionally reliable" internet shows that 8-gauge is good for ~55-60 amps (10-gauge less). If I remember correctly, my 3G alternators have double 6-gauge feeds.

    If you're planning on really using your 130A alternator, fab something bigger. Ace @185th & TV Highway should have everything you need very reasonably.

    Of course, YMMV :-)

    Mike
    Thanks Mike.. I actually bought the 4 gauge 3G power feed kit from LMR with their swap kit, so hopefully it should be adequate for what I will be doing. Its also got a hefty inline fuse as well.
    85 GT Hatchback, T-Tops. 2012 Coyote 5.0L Swap, T56 Magnum, GT550 Dept of Boost kit, with Eaton M122 SC, RAM 11" Powergrip clutch, BBK Long Tubes/OR X-Pipe, Flowmaster Axle Back, Stifflers DS Loop, and Rear X-member, AJE Tube Crossmember with AJE-Mod Mounts, 3.73 Posi 8.8, 5 lug Cobra 13" fr and 12.6" rear disc swap, 2004 Hydroboost Swap, MM SubFrame Connectors, MM Panhard Bar, MM front A-Arms, MM rear control arms, MM CC Plates, MM Coilovers w/Koni dampeners, MM Torque Arm (soon to be installed).

  8. #8
    FEP Super Member 84StangSVT's Avatar
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    Quote Originally Posted by tonysilver82 View Post
    That's for cars with rear defrost I think
    That and also used to power the convertible top.
    Brock
    1984 Mustang LX Convertible 3.8L V-6/Auto (SOLD)
    1984 Mustang GT Hatchback 5.0 V-8/5 Speed

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