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  1. #1
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    Weird reverse light fuse issue

    7-pin receptacle on an F-150. When I plug the trailer in, the reverse light fuse will blow. If I remove the fuse, plug the trailer in, and reinsert the fuse, no problems. So it seems that it is something that is happening when the plug goes in. It happens with different trailers, so it must be on the truck side. Anybody have this happen before?

    I've been just removing the fuse when hooking up, but that's obviously not the most convenient process.

  2. Electrical/Wiring/Trolling Motors Moderator CatFan's Avatar
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    #2
    Is the fuse the right size? Is this factory trailer wiring or aftermarket? Backup lights on the trailer?
    If you have integrity, nothing else matters. If you don't have integrity,
    nothing else matters.​

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    #3
    Quote Originally Posted by CatFan View Post
    Is the fuse the right size? Is this factory trailer wiring or aftermarket? Backup lights on the trailer?
    Fuse is correct size. Factory wiring. There are backup lights on one trailer and not on the other.

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    #4
    Sounds like you have a wire rubbing through that just isn't all the way through yet.

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    #5
    Quote Originally Posted by RiverZX View Post
    7-pin receptacle on an F-150. When I plug the trailer in, the reverse light fuse will blow. If I remove the fuse, plug the trailer in, and reinsert the fuse, no problems. So it seems that it is something that is happening when the plug goes in. It happens with different trailers, so it must be on the truck side. Anybody have this happen before?

    I've been just removing the fuse when hooking up, but that's obviously not the most convenient process.
    To clarify, it happens when plugging in, but before the truck is put in reverse? No matter what trailer you use?

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    #6
    Quote Originally Posted by mikeky View Post
    To clarify, it happens when plugging in, but before the truck is put in reverse? No matter what trailer you use?
    Correct. Once it's plugged in and I put the fuse back in, it works fine.

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    #7
    Quote Originally Posted by Bullet[BS] View Post
    Sounds like you have a wire rubbing through that just isn't all the way through yet.
    Yup. I'm gonna go with a chafe or a melted bulb socket.

  8. Electrical/Wiring/Trolling Motors Moderator CatFan's Avatar
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    #8
    Thought about it a while, and the only idea I can come up with is a bad connector on the truck.

    To test it, I’d get a 7 pin connector adapter that isn’t connected to a trailer and try plugging it in to the truck while the fuse is in place.
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  9. Electrical/Wiring/Trolling Motors Moderator CatFan's Avatar
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    #9
    Quote Originally Posted by bassboat1 View Post
    Yup. I'm gonna go with a chafe or a melted bulb socket.
    On both trailers?
    If you have integrity, nothing else matters. If you don't have integrity,
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    #10
    What is your typical scenario when hooking up? Truck running, not running. Is it dark out and running lights on?

    Duplicate scenario without hooking up then check to see which pins are hot. Gotta have a hot wire to blow a fuse. Is constant hot wire hot when truck isn't running?
    Last edited by mikeky; 05-31-2023 at 10:52 AM.

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    #11
    Quote Originally Posted by CatFan View Post
    Thought about it a while, and the only idea I can come up with is a bad connector on the truck.

    To test it, I’d get a 7 pin connector adapter that isn’t connected to a trailer and try plugging it in to the truck while the fuse is in place.
    Good idea...did that and the fuse did not blow.

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    #12
    Quote Originally Posted by mikeky View Post
    What is your typical scenario when hooking up? Truck running, not running. Is it dark out and running lights on?

    Duplicate scenario without hooking up then check to see which pins are hot. Gotta have a hot wire to blow a fuse. Is constant hot wire hot when truck isn't running?
    Not running, lights off (unless, I suppose, there are still lights on for the few seconds after turning the truck off). I did not find any hot terminal on the connector when the truck was off.

  13. Electrical/Wiring/Trolling Motors Moderator CatFan's Avatar
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    #13
    So listing the facts:

    Fuse is the correct size.
    It’s not a trailer problem.
    It doesn’t blow when hooking up an unwired connector.
    Nothing hot on the trailer connector before hooking up.
    It only blows while hooking up.

    Seems to me there has to be something hot or the fuse wouldn’t blow. Does your truck have an electric brake controller? Have you tried hooking up the trailer connector without hitching the trailer or connecting chains?
    If you have integrity, nothing else matters. If you don't have integrity,
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    #14
    On my F150 the lights come on for about a minute every time you open or close a door. So you could have lights on momentarily with the truck not running but then when checking the connector with a meter a moment later you'd find all the contacts off. Just something to keep in mind.

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    #15
    I will try connecting the lights without the hitch on the ball to see what happens. The thing that I can't understand is why everything functions fine if I remove the fuse, plug in the lights, and then put the fuse back in. If it was a chafed wire or something, wouldn't the fuse blow at some point while towing?

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    #16
    Quote Originally Posted by RiverZX View Post
    I will try connecting the lights without the hitch on the ball to see what happens. The thing that I can't understand is why everything functions fine if I remove the fuse, plug in the lights, and then put the fuse back in. If it was a chafed wire or something, wouldn't the fuse blow at some point while towing?
    I'm guessing something is happening during plug-in, but when the plug is completely seated it is past the problem area.

  17. Member wmitch2's Avatar
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    #17
    I'm thinking it's the Trailer Connector plug on the truck. Sounds like the movement from when you plug in to it, it is shorting between a hot and a ground, then somehow corrects it once it is in and then works fine after inserting the fuse. Could be a bad pin or a loose wire connection.
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