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  1. #1
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    New Holland TC48DA

    Default F150 Trailer Wiring Problem

    I need some help with my F150 trailer wiring. I am in the process of re-wiring a trailer and I hooked the new 7 way RV pigtail for the trailer to my truck trailer plug. I installed a brake controller with no problems but when I was trying to identify the function of each wire in the new pigtail, I couldn't get the turn and brake wiring to work. All the other 5 wires on the plug work perfectly, but I don't seem to have any brake light voltage or Rt. and Lft. turn signals. I first looked at all my fuses on my truck to see if any of them were blown, but they all checked good. I then disasembled the trailer plug on my truck and looked for broken or damaged wires in the plug. Other than a few small nicks on the wires, the plug looked good. I taped the nicks and replaced the plug. The brake and turn signals work fine on the rear of my truck. Doesn't the trailer wiring splice into the truck wiring? I inspected the wiring up until it merged with other wires going into my frame and didn't find any problems. It seems odd that both my Rt. and Lt. turn signal/brake wires would go out together. Is there any other relays or flashers that could be causing my problem. I don't want to dig into wiring harnesses in my frame, if I can help it.

  2. #2
    Elite Member
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    Default Re: F150 Trailer Wiring Problem

    Have you tried probing the truck plug itself with a test light or volt meter ?
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  3. #3
    Super Star Member Diamondpilot's Avatar
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    Jinma 254/284 Ford 861 Powermaster at work

    Default Re: F150 Trailer Wiring Problem

    Do as others have said and check with a test light at the trucks plug first. The wiring on the truck, if a late model like 97 or newer, is all sealed and just plugs in the factory wiring if oem.

    Chris

  4. #4
    Gold Member Hematite's Avatar
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    Default Re: F150 Trailer Wiring Problem

    You probably know this already, on the F150, the ignition switch has to be "ON" (engine running) for all the 7 way plug functions to work. I'm not sure if this is the source of the problem, though.
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  5. #5
    Super Member Inspector507's Avatar
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    Default Re: F150 Trailer Wiring Problem

    On some F150's there are two relays that need to be installed in the fuse/relay box under the hood to get those lights to work. I think one is for the battery charge function, one is for the lighting.

  6. #6
    Veteran Member
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    North Central Arkansas
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    John Deere 4520,

    Default Re: F150 Trailer Wiring Problem

    On Ford pick-ups there is a seperate relay/fuse for the trailer lights Look in the book that come with the truck. there is a listing of fuses and relays by number. then same page or close is the trailer listing of fuses. This has caused confusion on several goose neck trailer connections when driver leaves connected the lights cable and disconnects the trailer and drives off.
    For me the last time was in a parking area near Corning N.York and 20 Deg. temp blowing wind and State Police sitting in idleing car awaiting for us to repair before allowing to travel toward Penn. about 2 in the morning. took forever to locate a bad fuse.
    We now disconnect our own connector help is nice but some times causes problems.
    ken

  7. #7
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    New Holland TC48DA

    Default Re: F150 Trailer Wiring Problem

    I did check for voltage at the plug using a meter, with the truck running. I will try and locate the relay your refering to. The tail lights, reverse lights, trailer brakes and Pos. and GND all work. Is there a seperate relay or fuse for the trailer brake/turn lights?

  8. #8
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  9. #9
    Member
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    Default Re: F150 Trailer Wiring Problem

    Thanks for the information. That may just be my problem. I didn't realize I needed to look for another fuse box. My truck is a 98 F150 and it doesn't show another fuse box in the owners manual.

  10. #10
    Super Member radioman's Avatar
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    Default Re: F150 Trailer Wiring Problem

    Quote Originally Posted by rah6965 View Post
    Thanks for the information. That may just be my problem. I didn't realize I needed to look for another fuse box. My truck is a 98 F150 and it doesn't show another fuse box in the owners manual.
    yup - same here. my owners manual didnt show another fuse box. The fuse box in dash of my s-10 blazer doesnt have anything to do with the trailer. There is another fusebox in the engine compartment that has fuses for trailer wiring. Found out the hard way when one light wasn't working.

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