help trailer brakes locked up at 40mph
 

I bought a brand new big tex equipment trailer it has seven prong plug and my truck has a six prong so the dealer installed a seven on truck. Lights all worked but when I went to take off the brakes were locked up and the brake controller (which was installed by previous owner ) which is the kind that has the green light that turns to red was stuck on green and would not turn red. After unplugging it the brakes released and everything worked until I got 10 miles away and the brakes locked up at 40mph I unplugged them and drove home with no lights. Got home plugged in lights and the light on box stayed green even when applying the emergency overide switch. Then went back 10 min later and everything started to work.Any Ideas I assume that it is not the trailer It is brand new and was the first time it was on the road.

Electrical issues are always decieving, 1st physically make sure your truck plug is absolutely correct, then check the entire trailer harness. I know that your trailer is new, but don't assume the problem is not there, I have seen plenty a new trailer with crushed or shorted wires straight from the factory.
It sounds like some wires are misconnected or shorted causing you to get a positive signal to the brake circuit without a brake light signal. As to the specific cause, it will take time and physically untaping or disconnecting wireing to eliminate as you go. Just check your truck independantly then work the trailer.

Good luck.

Concur with Hvytrkmech; I picked up a brand new 4-horse GN in Caldwell, Idaho. Hooked up - brakes locked. Mismatch in wiring. Probably my truck, but took me 20-minutes getting it sorted out before I could get underway. Check to make sure that both plugs are correctly wired before troubleshooting anything else, would be my advice.

Good advice above. To me it sounds like it may be intermittent. I would disassemble both connectors and see if any of the wires are loose and touching others.

6 way plugs are not standardized. Horse and RV pinouts have brake and battery feed swapped.

http://www.etrailer.com/faq/wiring.asp

It is also important that you have a ground wire through the plug and don't rely on ground through the hitch.

Yup - as I found out...

By any chance is your truck equipped with an isolator for charging an RV battery? could be the guy hooked up auxiliary battery wire to trailer brakes. It could take about 10 miles to recharge truck battery completely. Then it switches over to recharge trailer battery, which charge wire might be mistakenly hooked to your brakes?

well after putting new brake box on truck we found out it was faulty wiring on the brand new trailer go figure.

My H&H trailer had a wire come loose in the junction box that caused the brakes to lock. It was about 3 months before it showed up. Fortunatly it didn't do while driving but just after I backed it into the driveway. After I unhooked the brake lights stayed on. Needless to say it happens.

Had the same problem with a brand new Big Tex trailer. The brake wire was never crimped inside the trailer harness and the ground bolt was less than finger tight (like someone put it on by hand and then never tightened it down afterward). [verymad]

I guess Big Tex doesn't make a habbit of checking their trailers and wiring before they leave the factory. [nonono]

same problem the brake wire was dangling inside the box but it also had a broken wire in the harness between the box and the plug.