just got a new boat and cannot really back it up because the brakes lock up when you start backing up. It worked perfect when the guy i bought it from took me for a test drive. Anyone ever have this problem?

Yes. 2 solutions: 1. Pin the tongue when backing. 2. Buy and install an electric bypass swith for surge brakes.
Most likely the guy you bought it from had the switch on his vehicle.

Most of these trailers have a 5 prong plug. If your trailer has the 5 prong plug and your truck does too then check your fuse or backup wiring. When you put the truck into reverse its supposed to release the trailer brakes.

i figured when you put it in reverse it was suppose to release the brakes. fuses are good so im guessing there is a short somewhere

Check the plug for a "hot" backup before you do anything else. Then work your way back. Do you have the 5 flat or 7 round RV? If you have the 7 round it might be wired wrong, I've seen a few wired differently. Not sure why since its a pretty standard order but it happens. But as mentioned in the other post earlier, you should have a lockout key for emergencies to keep the brakes from actuating. Might have gotten lost if you don't have one dangling on the tongue.

Make sure your trailer plug is plugged in correctly and making contact first. Sometimes it is not plugged in all the way.

--------------------------------------------------------------------------------

A "fine" point of operating surge disc brakes with a solenoid valve for backing up is realizing that the solenoid operates a valve that shuts off brake fluid flow from the actuator to the calipers. It does not release pressure, at least not on my trailer. Consequently, when you put your tow vehicle into reverse after stopping, if the trailer brakes were on when you stopped, they're still going to be on when you back up, even though the solenoid is energized and the valve is closed. After stopping you need to pull ahead and stop very gently so the trailer brackes don't engage, then shift into reverse. That way, the trailer brake lines are not pressurized when the solenoid valve is energized and flow will be shut off to the calipers. I've seen lots of guys with larger tow vehicles not even notice that their brakes were still engaged when they backed up. Doing so, they burned up brake pads very quickly. Just my experience. Hope it helps someone.

I found on my 2004 Ford F-150 that the purple wire (back-up) wire was not connected. Hooked it up and works well now.

IF there are back up lights on your trailer, and when you put the tow vehicle in reverse, do the lights come on, if not then there is no power to the brakes, easy check