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Wiring Woes

Discussion in '6.9L IH & 7.3L IDI Diesels' started by gandalf, Jun 19, 2019.

  1. gandalf

    gandalf Senior Member

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    I've found a problem in my truck's wiring. It's going to drive me right around the bend.

    I've recently bought an enclosed cargo trailer. I, of course, did a light check on the trailer. All lights work except the left brake light and left turn signal. The left tail light is fine, and all lights work on the right side. Running lights and such are good. All lights are good with that one exception.

    The jack on the truck is a 7 pin round traditional, flat pins. This style is dictated by the jack on the trailer. The trailer has electric brakes. The flat pin for left stop and turn light is dead, never receives power. Sounds like a simple fix, right? I call BS.

    I've checked all fuses, both under the dash and in the engine compartment. I pulled them all and tested with a multimeter. All fuses are good. I opened up the jack under the bumper looking for a loose connection. There was none.

    A point of interest here. The power distribution box, fuse box, under the hood seems to be from a '94 truck, according to the diagrams I've found. It has a different layout from what I was expecting. My truck is a '92, built in 11/91.

    What am I missing? Is there some place else to simple turn off that circuit?

    Can you tell how much I dislike automotive electrics?
     
  2. Clb

    Clb Another old truck Supporting Member

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    First Trace and loom for p/o owner fubar.
    And then meter those wires rear to front 1 at a time for continuity first.
    Then check the actual contacts male to female....
     
  3. ifrythings

    ifrythings Full Access Member

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    Check if your getting power to fuse G first, that will tell you if it’s cab side or frame harness side. Ford did something off the wall with the trailer turn signal wiring, they go from the turn signal switch through the firewall to the frame harness, tap off and run it back through the firewall over to the other firewall plug to the engine bay harness, then to the fuse box and back to the firewall again, into the cab and right back out the firewall again to the frame harness then to the back of the truck to a plug then finally to the 7pin trailer plug...

    A good place to check for po hacks is right at the front of the box, lots of people like to t-tap (worst things ever) right there for a slide in camper or 5th wheel plug.
     
  4. gandalf

    gandalf Senior Member

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    ifrythings, that sounds like a frigging nightmare. Is that one of Ford's "Better Ideas"?

    Nowhere are my fuses labeled by letter. If I do a simple alpha-numeric conversion on the box under the hood, g=7, "trailer left-hand stop/turn lamp. I know the fuse itself is good, but I haven't checked whether it is actually receiving power. I'll do that this afternoon.

    Could I perhaps go a far simpler route, and tap into the proper wire at a tail light on the truck? Those bulbs are two filament bulbs, regular tail lights, and stop/turn. There must be a separate wire for each. Couldn't I just tap into the stop/turn wire and take it to the trailer jack, disconnecting the stop/turn wire from the front? Theory tells me that should work.
     
  5. ifrythings

    ifrythings Full Access Member

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    You could tap into the rear lights, just if something happens it will blow the fuse for all your lights instead of the fuse just for that side trailer light.
     
  6. gandalf

    gandalf Senior Member

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    The #7 fuse, under the hood, "left stop and turn" has power. It has power when the left turn signal is on. Without the turn signal it seems to not have power.

    The 5 pin round jack, located in the bed at the rear tailgate, has power for the left turn/brake. I don't know where that power is coming from, the trailer circuit or the truck light circuit.

    I'm learning to hate auto electronics more with each passing minute.
     
  7. CDX825

    CDX825 filtration nut

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    Trace the wires from the trailer plug forward on the truck. I'd bet you have a broken wire some place.
     
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  8. Thewespaul

    Thewespaul Supporting Vendor Supporting Member

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    CD150BA8-3A7D-4929-888E-3315E1CAF345.jpeg 2336F0A1-E78C-4243-AF21-EFD2CDEF6809.jpeg B4E8B2C4-7B39-4FF7-9288-858B553B386B.jpeg
     
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  9. gandalf

    gandalf Senior Member

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    I think I may be gaining on it. There is a 7 pin connector by the rear bumper, the last thing before the trailer jack. Pictures to follow. I can get continuity, of some sort or another (multimeter is a POS) on 3 of the four wires between that and the jack. One wire SEEMS to have no continuity. I guess I'll have to open up the jack again for a closer look. That means unwrapping all the tape and pulling the jack, after I disconnect the batteries of course.

    IF that is the problem and I have to replace that wire (the whole little harness is 12-18 inches), I'll have a choice. I can go to Pick-n-Pull and fine a "new" harness, or I can cut that wire close to the connector and put on a spade connector and new wire from there to the jack. Or maybe the problem is in the 4 wire connector itself, or in the 7 pin jack. Either one is possible, but a PIA.

    Good thing I have plenty of decent electrical tape.

    Neither picture file will upload. They're apparently too big, at 4.6 and 4.75 Mb.
     
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  10. Clb

    Clb Another old truck Supporting Member

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    My 2 favorite things in the world to work on are....

    P.O. cobblefab work.
    And
    P.O.
    ELECTRICAL FUBAR WORK!











    PERIOD -Lame:rtfm
     
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  11. gandalf

    gandalf Senior Member

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    Done!!! All the trailer lights are working.

    Along the way I:
    1) Removed/eliminated a trailer jack at the rear bumper--7 pin round, round pins. I removed and replaced a shitload of Scotchlock connections during that process.
    2) Moved the left turn wire to the correct position on the 7 pin round, flat pins, jack.
    3) Replaced a couple blown fuses.
    4) Replaced the left light unit on the trailer.

    And it still didn't have left turn or brake light.

    5) Disconnected a wire going into the door panel at the rear of the trailer. It must be for a license plate light. I couldn't see any license plate light, though. There's no other possibility on the swinging door.

    I disconnected that wire and the left turn/stop light worked.

    Have I mentioned how much I hate auto electrics?
     
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  12. chillman88

    chillman88 Supporting Member Supporting Member

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    I had something similar infuriate me on my other truck. I suddenly had no dash lights, fuses were fine. Got mad at it and took it to the dealer. $115 for them to unhook an aux light from the trailer plug...

    WTF who puts trailer lights on the same circuit as gauge illumination????

    Glad you got it licked!
     

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