Trailer brakes locking when headlights on
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Hey guys I am having this issue with my 2014 F150 STX. I just had the controller flashed by dealer that I installed. The trailer brakes work fine and until yesterday I had never been out late to were I wanted to turn my head lights on. As soon as I did the brakes locked up. I was confused and unplugged trailer. Then when I got to my buddys I was telling him and he tells me the trailer is wired wrong. I pulled the plug and it looks correct. All the trailer lights work correctly, so could it be an issue behind the plug? I did follow the wires back from the plug to the battery box for the break away switch. There is a bunch of wires tapped into there but I haven't traced them out to see if they have the trailer brake wire tapped into a tail light wire by accident.
#14
Welcome to FTE!
Question: did the truck *ever* tow with the lights 'On' (presumably headlights) and work normally with any trailer's brakes?
The first thing I check is the truck to make sure all the pins in the plug are good and getting voltage when appropriate. A simple multi-meter is good for this and a test-plug is a bonus.
If the truck checks-out as good, then focus on the trailer side by applying power one pin at a time with either a spare battery (including an inline fuse) or battery charger. By isolating one circuit at a time, it saves time by not ripping the whole wiring bundle apart.
Question: did the truck *ever* tow with the lights 'On' (presumably headlights) and work normally with any trailer's brakes?
The first thing I check is the truck to make sure all the pins in the plug are good and getting voltage when appropriate. A simple multi-meter is good for this and a test-plug is a bonus.
If the truck checks-out as good, then focus on the trailer side by applying power one pin at a time with either a spare battery (including an inline fuse) or battery charger. By isolating one circuit at a time, it saves time by not ripping the whole wiring bundle apart.
#15
Since the headlights don't really have a direct circuit to the trailer, it has to be the marker light circuit that is crossed to the trailer brakes, if that is the only circuit that activates the trailer brakes (I am assuming the trailer brakes work without a problem otherwise?)
I agree with what Jay is suggesting. First verify that the trailer brake pin on the seven pin on the truck goes hot when you turn on the maker lights. If it does, the problem is most likely the wiring in the seven pin on the truck itself, unless someone has messed with the wiring in the past. I posted a while back about one I worked on where the trailer brakes activated when the left turn signal was used, but that wiring was a real mess and the problem was obvious.
Steve
I agree with what Jay is suggesting. First verify that the trailer brake pin on the seven pin on the truck goes hot when you turn on the maker lights. If it does, the problem is most likely the wiring in the seven pin on the truck itself, unless someone has messed with the wiring in the past. I posted a while back about one I worked on where the trailer brakes activated when the left turn signal was used, but that wiring was a real mess and the problem was obvious.
Steve