Hello, I am having problems with the brakes on my trailer with my truck. I can apply power straight to the brake wires and they lock, but when I plug it into my truck, they keep spinning. I measured the plug and get about 4volts with the brake controller turned all the way up. My question is, what should the output of the plug be, or what could be causing my problem, thank you.

some controllers are smart enough to know there is no load, so you really cant trust those numbers. you make sure you get a good ground path through the truck?

I hooked the trailer up to the truck and took it around the block. when I would hit the brake pedal, nothing, but when I hit the lever on the controller, it locked my brakes up. I am wondering if maybe the brakes are to loose and the 4 volts coming from the controller aren't enough to stop the brakes.

that sounds like something messed up with the controller, if you have the gain adjusted up high