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Old 10-04-2011, 11:46 PM   #1
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Default trailer lights

I have 2007 ford f150, I was pulling a boat and noticed the tail lights, and running lights on the the trailer were not working. If I hit my brakes the tail lights would would light up, but otherwise won't. I turned my hazard lights on and the tail lights work on the trailer. My tail lights on my truck work, but I can't think of what the problem could be. It is my neighbor's boat and when he uses his truck everything is working. Could it be a fuse? any ideas will help.
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Old 10-05-2011, 01:27 AM   #2
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There are wiring standards for each type of trailer connector. Sometimes people don't research the wiring standard and create their own.

On my 2003 F150 with the factory towing package and factory trailer wiring the trailer lights are fused independently from the truck lights. That should be illustrated in your owner’s manual. On my truck the trailer fuses are under the hood in the power distribution box. There are also trailer towing relays for trailer back-up lights, electric brakes, and 12v trailer battery charge. All that's in the owner’s manual, good luck!
If you don’t have an owner’s manual you can check each fuse with a 12 volt test light.
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Old 10-07-2011, 07:48 PM   #3
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Your problem is with grounding. A wire someplace on the trailer has cracked or worn the rubber cover around the wire, allowing the copper wire to make contact with the trailer.

You can use a test light to try to isolate the general area of the short, but best to just get on your back and examine the wiring and find the short. Tape it up and you should be good to go.
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Old 10-08-2011, 09:33 AM   #4
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+1 on the bad grounds. Funny things happen when there is a bad ground. Before I connect any strange trailer to my vehicle, I plug in a spare pigtail to the trailer and use my multimeter to check the ground and a battery or battery charger to check the light circuts.
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Old 10-09-2011, 10:47 AM   #5
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You can isolate the problem and check your vehicle with a very inexpensive tester that's available at Harbor Freight or most parts stores. Here they have a 4 pin but also have a 7/8 pin if you tow larger trailers with electric brakes.

It truly is a time saver to be able to verify the vehicle is 100% quickly. Then you can move on to checking grounds and circuit continuity on the trailer.
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Old 10-09-2011, 04:56 PM   #6
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Could as simple as the ground wire at or around the plug. It could also be there is no ground wire connected and it is deluging on the ball/hitch connection to provide the ground. My boat trailer had a ground bolted to the frame right at the hitch, the crimp connector broke and I had the same problem you described and when I hit bumps the lights would flicker..
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Old 10-11-2011, 10:19 PM   #7
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Always check your fuses.
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Old 08-27-2012, 01:51 PM   #8
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I am having a similar issue on my 97 f150 the thing is that eariler this year when I was towing my boat with my 01 mazda b3000 (AKA ford ranger)with the factory trailer wiring all the lights worked fine so I know the trailer wiring id good. I was towing it with the f150 a few weeks ago and I noticed that the running lights and tail lights were not working when I turned the headlights on on the truck but the brake, turn, and hazard lights worked fine. any ideas where to start looking in the wiring on the truck?
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