Truck won't back up horse trailer...thoughts?

I must apologize, I am not sure what I was thinking, well reckon I wasn't...lol

I love a horse trailer mystery. It will be interesting to hear what it was. But I bet you're on to it already with the brake box/wiring. Good luck

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For we used to ask when we were little, thinking that the old men knew all things which are on earth: yet forsooth they did not know; but we do not contradict them, for neither do we know.

It can also be brake problem with the wiring correct. Particularly if these are drum brakes. They can be assembled wrong so the self actuation locks them as soon as they reverse rotation.

I would love it if it were as simple as a crossed wire.
But if it were just the trailer's brakes on, the truck could spin the tires when backing up, pushing against the trailer. Sounds like the motor races, but the truck sits still. Not good.

Mystery solved! I just hitched up the truck and trailer and drive the trailer all over the pasture in both forward and reverse No resistance at all backing up. I left the electric plug disconnected, so it's gotta be crossed wiring in the plug. Nothing at all has been done with the trailer brakes recently, so no way could it be that the trailer brakes were put together wrong.

I am positively delighted that it's not something more serious. Now the only issue is to figure out how to rewire the plug myself. The guy who did the work originally is hours from here, so not worth the trouble of taking it all the way to him to fix it.

I looked and I don't have the manual that would have come with the brake brain. Any tips on how to uncross the wires?

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"Perhaps I'll have them string a clothesline from the hearse I am in, with my underwear waving in the breeze, as we drive to the cemetary. People worry about the dumbest things!"
by Wendy

................Buy yourself a 12 volt Dc test light ! It will have an alligator clip that you connect to a metal ground near the rear plugin on the truck ! You will probably have a 7 pin round connector . Start the truck and turn on the dimmers(no headlights) , stick the sharp metal end of the test light into each individual hole , you should have .....right turn(1) , left turn(2) , brake lights)(3)both turn signals working together) , brake power wire(4) which is obviously connected to the wrong wire in the truck end of the plug , dimmer lights(5) , ground wire(6) , and a 12vdc power wire to recharge a battery on the trailer(7)............that's seven connections !!!!!Please note.....my numbering does NOT correspond to the CORRECT pin numbering on the Connector! I'm thinking the mistaken connection is on the pickup end of the plugin . , fordy

Thank you! This sounds easy enough Will try this and let you all know how it goes.

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"Perhaps I'll have them string a clothesline from the hearse I am in, with my underwear waving in the breeze, as we drive to the cemetary. People worry about the dumbest things!"
by Wendy

Good luck but be cautious. I have had the brake box itself be a problem.
Also, you might be able to find installation instructions online depending on the manufacturer.

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For we used to ask when we were little, thinking that the old men knew all things which are on earth: yet forsooth they did not know; but we do not contradict them, for neither do we know.

................You should really have a friend watch the test light while you do the lt , rt, brakes , trailer brakes etc . Google '7' pin trailer connector and it will show you the proper color coding for each wire on the truck and the trailer . There mayBE a difference in wiring color between the truck connector and the wiring cable on the trailer ! , fordy

i have very often found that many people wire the center post to the brakes on the trailer when its really an accessory wire. in some trucks its a hot wire... ment to supply power to charge a battery or have power to a lightbulb to see at night.

id start there. have someone help you and draw a chart once you get that light tester... that way you can identify what is where. you can then use an extra wire to goto each one on the trailer to find out which 2 are wrong. saves unscrewing those tiny screws and losing them =(

good luck!

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A friend is coming to help me with it tomorrow. Between the two of us, I think we can get it sorted

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"Perhaps I'll have them string a clothesline from the hearse I am in, with my underwear waving in the breeze, as we drive to the cemetary. People worry about the dumbest things!"
by Wendy

.............I should have mentioned that you can eliminate (4) wires by simply plugging in the connector and testing , RT , LT , Brake lights , and ground ! That only leaves (3) , left to check , although the trailer can be grounded (not very well) thru the metal to metal contact on the hitch to ball connection . , fordy

I second him being wrong, my dcab 4x4 Tacoma is rated to pull 6000 pounds.

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Wiring is always a trouble spot.

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We will meet in the golden city, called the New Jerusalem,
All our pain and all our tears will be no more.....

sounds like electric brake trigger signal wire was hooked to backup light wire instead of break light wire. If so the trailer brakes would not work when break peddle was pressed, instead they work when reverse is engaged.