First, make sure you have 12v to the blue wire at the solenoid, with the tow vehicle key on, and in reverse. You should see 12v when the backup lights on the tow vehicle are on. If no voltage, check your wiring at the plug. If you have someone to help you that can shift the vehicle in and out of reverse (without the motor running), you should hear a faint click and you also should be able to feel the plunger engage inside of the coil. If you have voltage but no click, replace the solenoid. The function of the solenoid is to divert the fluid in the system from going toward the brakes, by diverting it back to the reservoir. If you unplug your trailer and back up a slight hill until the brakes engage, then plug in the brakes and put it in reverse, it should release the brakes. To replace the solenoid, use snap ring pliers to remove the snap rings on the large pins. Remove the brake line and disconnect the blue wire at the solenoid by disconnecting it from the wiring loom. Once the pins are removed, slide the actuator out the front, replacing the pins as the inner member clears the body of the outer member. Replacing the solenoid is now just a matter of unscrewing it from the master cylinder after removing the zip tie and return line. Screw the new solenoid on and reverse the order to install. Now bleed the brakes. Remember, air bubbles go up, so lower the nose of the trailer before bleeding. The air will naturally travel toward the bleeders and make your bleeding easy.