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Old 10-19-2015, 05:29 AM   #1
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Trailer Brake/Turn signal lights

I have a 2008, F-350, Super Duty, Dually, V10, 2 wheel drive. I am having a problem and can't find the fuse for this.

My brake/turn lights work on the truck, but will not work on the trailer (any trailer). Like I said, every other light works just fine, even when hooked to the trailer the truck brake/turn lights still work, but the the brake/turn lights won't work on the trailer itself.

I have tried looking at several of the fuses under the glove compartment, but don't see any bad ones (I did use a tester).
Is there another fuse panel? Any idea what the fuse would be named? I went through the owner's manual and anything with the word "Brake" in it I checked.

I was on the side of the road when I was doing this, after another driver told me I had no brake lights and he almost slammed into me when we all had to "Stop short" due to traffic. So, I didn't get to do a complete, thorough check. But, I am not a mechanic, don't want to do too much poking around either. I hate to take it do a dealer for a "blown fuse" if that is all it is. If it's it's something more then I have no problem paying a professional to fix it right. I just feel I should at least know for sure it's not a blown fuse first. Plus, if it is, then I need to know where to look next time and to have spare fuses/relays in the truck.

Thanks in advance

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Old 10-19-2015, 06:50 AM   #2
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Fuse box in the engine compartment.

There is trailer fuses in there.

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Old 10-19-2015, 06:55 AM   #3
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Engine compartment.
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Old 10-19-2015, 08:00 AM   #4
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Start looking for power at the individual connector pins on the back of your truck and work your way forward. Several of us have had bad connections over the years at the pin itself depending on which function is at fault. Download a wiring diagram of the 7 pin connector to see which wires(pins) are stop and turn lights.
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Old 10-19-2015, 11:40 AM   #5
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Ford has separate fuse box under the hood for trailer lights. It should be near the master brake cylinder on the left (driver side) fender well. That has happened to me!!!!
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Old 10-19-2015, 11:50 AM   #6
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Agree with other posters, check fuse box, left side, under hood. When you get a chance, photocopy the fuse location/identification in the owners manual and put it inside your fusebox. They wwere not labelled on the last two I worked on. Then get a couple of spares and keep them handy. If they blow again, have a close look at your lamps, as if they short, they take out your fuses again. Usually the brake/turn ones.
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Old 10-19-2015, 12:07 PM   #7
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Check your plug and scrape off your leads with a knife. Has happened to me many times and this has always worked.
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Old 10-19-2015, 12:27 PM   #8
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I'm all for checking each terminal on the 7-way connector first, then work forward if any terminal(s) are not working. I've been through this on many trucks to find one or more terminals are not working. I have found where the wires terminate at the 7-way plug that the termination was not good. I found the left blinker terminal not working on a 2007 GMC I had. The dealer found a bad terminal connector at the fuse box under the hood on that one. On my 2014 GMC I found that the 12vDC+ terminal was not working straight off the lot. After the dealer replaced three (3) fuses for the 12vDC+ wiring then they had the truck for two (2) days and found a bad "Trailer Control Module". They replaced it and all has been well since. Truck wiring is not a specific science. One can learn a lot by obtaining a repair manual from a local auto parts store with electrical systems schematics, having a volt/ohm meter and learning how to troubleshoot these problems.
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Old 10-19-2015, 12:46 PM   #9
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While you are in the fuse block, check for the fuse and relay for the +12V Aux pin on the 7-pin trailer connector. Usually these are not installed but may be on glove box.

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Old 10-20-2015, 04:14 AM   #10
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Thank you all....
It was a fuse under the hood.
Thinking back I had hooked up to a "Dump" trailer about 6 months ago, I got a warning on my dash saying the trailer lights weren't right. It must have blown the fuse then. I hate helping "buddies" who don't maintain their equipment. With all of the Hi-Tech electronics in today's vehicles I hate to hook up to others equipment and NEVER give a jump to anyone, I carry a Jump Box for that.

I went ahead and checked everything else out and it's all working now.

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light, trailer, brakes

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